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THE RELATION OF WATER TO THE 

BEHAVIOR OF THE POTATO 

BEETLE IN A DESERT 



A DISSERTATION 

SUBMITTED TO THE FACULTY 

OF THE OGDEN GRADUATE SCHOOL OF SCIENCE 

IN CANDIDACY FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 

DEPARTMENT OF ZOOLOGY 



BY 

JOSEPH KUMLER BREITENBECHER 



Private Edition, Distributed By 

THE UNIVERSITY OF CHICAGO LIBRARIES 

CHICAGO, ILLINOIS 



Reprinted from 

Publication 263 or the Carnegie Institution of Washington 

pp. 341-84 



XTbe Tllniversitp of Cblcaao 



THE RELATION OF WATER TO THE 

BEHAVIOR OF THE POTATO 

BEETLE IN A DESERT 



A DISSERTATION 

SUBMITTED TO THE FACULTY 

OF THE OGDEN GRADUATE SCHOOL OF SCIENCE 

IN CANDIDACY FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 

DEPARTMENT OF ZOOLOGY 



BY 

JOSEPH KUMLER BREITENBECHER 



Private Edition, Distributed By 

THE UNIVERSITY OF CHICAGO LIBRARIES 

CHICAGO, ILLINOIS 



Reprinted from 

Publication 2O3 of the Carnegie Institution of Was)iington 

pp. 341-84 



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THE RELATION OF WATER TO THE 

BEHAVIOR OF THE POTATO 

BEETLE IN A DESERT 

BY 
J. K. BREITENBECHER 

OF THE BIOLOGICAL LABORATORY OF WESTERN RESERVE UNIVERSITY 



[Extracted from Publication 263 of the Carnegie Institution of 
Washington, pages 341-384.] 



CONTENTS. 

PAGE 

Introduction 343 

Instrumentation and conditions of experiment 343 

Materials 344 

Role of water in reproductive activity 346 

Experiments with soil moisture 348 

Experiments with evaporation rates 349 

Role of water in the preservation of life 350 

Relation of water-loss in insects when exposed to changes in the relative 
humidity of the surrounding medium, and its effect on the activities 

of such organisms 354 

Experiments upon evaporation, transpiration, and behavior 365 

Role of water in hibernation 366 

Entrance into hibernation 366 

Activities during hibernation 371 

Water relation of soils and hibernating beetles 371 

Emergence from hibernation 372 

Summary and discussion upon the relation of water to hibernation 373 

Effect of changes in water content upon alterations in tropic activities 375 

Experiments upon the role of water in geotropism 376 

Relation of temperature to outgo and intake of water 377 

Metabolism and water relation 378 

General discussion upon the role of water in living things 379 

Summary and conclusion 381 

Bibliography 382 



THE RELATION OF WATER TO THE BEHAVIOR OF 
THE POTATO BEETLE IN A DESERT. 



INTRODUCTION. 

In a series of experiments maintained by Professor Tower to determine the 
action of the Tucson Desert upon evolutionary processes in chrysomelid beetles, 
it was observed that soil-moisture, humidity, and the like played an important 
role in modifying the activities of these organisms when introduced into the 
arid region ; so, as a result of these observations, the author undertook a series 
of investigations to discover any possible connection between this water-relation 
and the reactions of the potato beetle, Leptinotarsa decemlineata (Say), when 
transplanted into the desert from a temperate habitat. 

A large stock of this species was sent to Tucson from Chicago in June 1911, 
so that comparative studies under different environmental complexes could be 
made. Three cultures were established in several open-air breeding-cages at the 
stations already equipped for Professor Tower at Tucson and Chicago. Two of 
these stations, which were arid in character, are designated as Tucson Station A 
and Tucson Station B, while the third one, known as the Chicago Station, was 
temperate and located at the University of Chicago. The former of the two 
desert stations was situated at the base of the northern slope of Tumamoc Hill, 
just within the flood-plain of the Santa Cruz River, at an altitude of 3,370 feet, 
while the latter was located on the shoulder of this hill, on which the Desert 
Laboratory is situated, at an elevation of 2,705 feet. The biological significance 
of the conditions at these stations, as indicated, is given elsewhere, and the 
problems dealt with concern the relations which exist between the activities of 
the beetles when allowed to reproduce at these localities and the changes pro- 
duced in the water-content of the animals through the action of the various 
environmental factors. 

INSTRUMENTATION AND CONDITIONS OF EXPERIMENT. 

At each station the evaporation rates were obtained by the Livingston at- 
mometers, and Friez self-recording thermographs were employed to measure 
the temperatures, air and soil, and the same maker's hygrographs were also 
used for the relative humidities ; these instruments were calibrated and stand- 
ardized fortnightly. The rainfall-readings were obtained from a standard 
weather bureau rain-gage at the Laboratory site. It is interesting to notice that 
the environmental data as recorded from these experiments showed for the arid 
complex that the greatest daily fluctuations occurred at Station A and the 
highest evaporation at Station B, while the lowest evaporation-rates and air- 
temperatures were at Station C. The Tucson region as a whole, when contrasted 
with the Chicago conditions, has a higher rate of evaporation, a lower relative 

343 



344 



Eelation of Watek to the Behavioe of 



humidity, a stronger light intensity, and a wider daily fluctuation in both air 
and soil temperatures ; excessive nocturnal radiations and convectional currents 
were also potent factors in the desert. 

Four seasons were apparent in the arid region : A winter rainy season extend- 
ing from November until April; a dry fore-summer season, from April until 
July ; a midsummer rainy season, from July until the middle of September ; and 
a dry after-summer season, from the middle of September until early in Novem- 
ber. At Chicago rain occurred throughout the year. The annual rainfall from 
several years' data was about 12 inches at Tucson and 30 at Cliicago. The 
monthly records for both stations are given in Table 1 for the three years during 
which these experiments were in progress. 

Table 1. 



station. 



Tucson . 



Ch icago. 



Year. Jan. 



191011.00 
1911|1.31 
1912j0.00 

19103.07 
1911 1.17 
19120.84 



Feb. 



T. 
0.99 
0.37 

0.89 
2.27 
1.57 



Mch. 



T. 
0.25 
2.12 



Apr. May. 



June. 



0.05' T. 0.22 
0.27 0.000.07 
0.28 0.32,0.61 



0.29 3.84 4.67 
1.453.033.37 
2.2012.55 3.97 



0.91 
2.54 

1.78 



July. 

4.20 
1.57 
3.00 

1.79 
2.65 
3.86 



Aug. 



4.65 
2.06 
0.98 



3.08 
3.72 
3.59 



Sept. 



Oct. Nov. 



0.62 0.08 
2.65 1.23 
0.01 1.78 



3.90 
4.03 
3.26 



1.79 
3.79 
3.52 



1.74 

T. 

0.00 

1.31 
3.27 
1.45 



Dec. 



0.06 
0.85 
0.39 

1.32 
2.54 

1.08 



Total. 



12.62 

11.25 

9.84 

26.86 
33.83 
29.67 



Note. — The rainfall records at Tucson were obtained from a standard Weather 
Bureau rain-gage at the Laboratory site. The Chicago data were taken from the 
records of the Weather Bureau. 



MATERIALS. 

The potato beetles were collected in May 1911, near Chicago, as they emerged 
from hibernation, and were allowed to breed there as a group-culture within a 
large cage filled with potato plants until late in June. A part of this material 
was then sent to Tucson, where it became the progenitor of the animals used 
in the majority of the experiments. Organisms when collected from nature are 
often hybrids, so that crossing of different generations may have taken place, but 
for complete breeding-records and life-histories of stocks used see Table 2, which 
shows that these materials reacted homozygously. A brief description of their 
activities follows. 

At Tucson Station A these stocks were received on June 26, 1911, and 
immediately bred as a group-culture, so that 1,328 adults were produced in 25 
days, giving generation I. After feeding upon the potato plants for a few days, 
these first-generation individuals were bred as a group-culture and produced 
generation II, numbering 2,312 progeny, in 26 days. Many of the beetles of this 
second generation provided the materials for a large number of the hibernation 
experiments which were carried on in 1911, but many of the emerged animals 
were allowed to hibernate during the winter of 1911-12 as stock for work during 
the following year. When, in June, water was added to the soil within the cage, 
the organisms emerged from hibernation as a group-culture, which in 29 days 
gave generation III, of 1,743 offspring. From this material 50 females and 
50 males were mated and allowed to breed at random, giving generation IV, of 
4,049 progeny, in 26 days. For the above data, see Table 2. 



The Potato Beetle in a Deseet 



345 



At Tucson Station B the parent group of 104 adults for this culture was 
received on July 15 and bred as a group -culture, producing 204 offspring in 
25 days, thus giving generation I. As soon as the adults from the first genera- 
tion appeared they were removed to another breeding-cage, but they immediately 
burrowed into the ground within the experimental cages and hibernated there 
until September, when they began breeding and in 21 days produced generation 
II, of 293 progeny. A few days after emerging from pupation all of the beetles 
went into hibernation without feeding, where they remained until the following 
summer, when, on May 31, 7 males and 16 females emerged and bred immedi- 
ately, giving generation III of 283 adults in 31 days. These were allowed to 
reproduce as a group-culture, giving in 31 days generation IV of 127 offspring. 

Table 2. 



Year, station, and 
generation. 



1911, 
1911, 
1912, 
1912, 
1911, 
1911, 
1912, 
1912, 
1911, 
1911, 
1912, 
1912, 



Tucson A, g. I 

Tucson A, g. II 

Tucson A, g. Ill .. 
Tucson A, g. IV... 

Tucson B, g. I 

Tucson B, g. II 

Tucson B, g. III... 
Tucson B, g. IV... 

Chicago g. I 

Chicago g. II 

Chicago g. Ill 

Chicago g. IV 



Duration of 
breeding. 



June 26- July 17 

Aug. 1-18 

Autumn of 1911 

July 8-29 

July 15-23 

Sept. 3-7 

Mav31-June20 
JulyI0-Aug.l2 



Period of 
oviposition. 



July 7-19 

Aug. 4-22 

June 4-15 

July 15-29 

July 17-23 

Sept. 3-7 

June 6-20 

July24-Aug. 12 

June 6-15 

Aug. 1-15 

June 2-19 

Aug. 1-15 



First 
stage larviB. 



July 12-21 

Aug. 10-26 

June 12-21 

July 17-Aug. 2 

July 21-29 

Sept. 5-11 

June 14-25 

July 27- Aug. 14 



Second 
stage larvae. 



July 
Aug. 

June 
July 
July 
Sept 
June 
Aug. 


13-27... 




16-31... 
15-28... 
20-Aug. 
23-Aug. 
7-19 


5 
2 


16-30... 
4-27. . . . 





Third 
stage larvae. 



July 17-31 

Aug. 22-Sept. 1 

June 18-30 

July 25-Aug. 8 
July 27-Aug. 6 
Sept. 11-21.... 
June20-July 10 
Aug. 12-29 



Year, station, and 
generation!. 



1911, 
1911, 
1912, 
1912, 
1911, 
1911, 
1912, 
1912, 
1911, 
1911, 
1912, 
1912, 



Tucson A, 
Tucson A, 
Tucson A, 
Tucson' A, 
Tucson B, 
Tucson B, 
Tucson B, 
Tucson B, 
Chicago g. 
Chicago g. 
Chicago g, 
Chicago g. 



p. I 

g II.... 
g.III... 
g. IV... 

g.I 

g.II.... 
g. III... 
K. IV... 

I 

II 

Ill 

.IV 



Pupa 
state. 



July 19-Aug. 1 
Aug. 26-Sept. 2 
June21-July 8 
July29-Aug. 11 
July 29-Aug. 8 

Sept. 12-22 

June25-July 15 
Aug. 14-31 



Emerged as 
adults. 



July31-Aug.l4 

Sept. 2-13 

July 4-16 

Aug. 8-26 

Aug. 10-18 

Sept. 19-29.... 

July 10-23 

Sept. 1-7 

July 1-20 

Se^t. 1-10 

July 10-12 

Sept. 4-20 



No. of 
adults. 



1328 

2312 

1743 

4049 

204 

298 

283 

127 



Adults 
hiberniateKl. 



None 

Over winter. . . 

None 

Oct. 1 

Aug. 18-Sept. 8 

Sept. 30 

None 

Sept. 2-8 

None 

Sept. 1-10 

None 

Sept. 20-22.... 



Duration of 
life cycle. 



25-26 days. 
22-29 days. 
28-30 days. 
24-28 days. 
25-26 davs. 
20-22 days. 
33-35 days. 
26-36 days. 
25-35 days. 
25-30 days 
23-38 days. 
34-36 days. 



Early in September all were in hibernation and remained in the ground during 
the winter. On the other hand, at the Chicago Station, the original wild parents 
were allowed to breed as a group-culture, and gave generation I in 30 days. 
These adults bred as a group-culture and produced generation II in 33 days, 
which now hibernated during the winter from September until May, when they 
reproduced and gave generation IV in 35 days : for the above data, see Table 2. 
The animals for experiment were reared upon potato plants in cages of uni- 
form size (6 by 6 by 6 feet), with sides of wire-netting, 16 meshes to the inch. 
These cages were furnished with wooden bottoms (6 by 6 by 3 feet), which were 
filled with a mixture of equal parts of adobe ^ and sand. This mixture proved to 



^ At Station A, where this soil was obtained, the adobe consisted of a clay loam, 
which constituted the soil-mass of the river flood-plain. This soil was about 8 to 9 
meters deep and rested on sand and gravel. Livingston (1910) found it to have a 
water-holding power of about 18 per cent of its dry weight. The sand used in all 
experiments was obtained from an arroyo near at hand and had a water-holding 
power of about 39 per cent of its dry weight. 



346 Eelation" of Watee to the Behaviok of 

furnish favorable conditions for plant growth as well as pupation and hiberna- 
tion activities. 

The condition of the experiment required that a certain routine be repeated 
each time, and some of the most ordinary methods follow. The rates of evapora- 
tion were obtained with the Livingston atmometers, which were cut down to a 
cone of 50 mm. in length to avoid an error introduced by having shellacked 
bases. These were standardized on the rotating machine in the Genetics Labora- 
tory at Chicago, and showed after standardization a maximum range of 3 per 
cent from the normal. The dry weights of the insects were obtained as follows : 
first by killing them in potassium cyanide, and desiccating them at a constant 
temperature in a vacuum over concentrated sulphuric acid until the dry weights 
became approximately constant. The soil samples when collected were placed 
in glass-stoppered weighing-bottles and carried to the laboratory, where they 
were weighed and dried at a constant temperature of 100° C. The tropic reac- 
tions were tested in the constant-temperature room (18° to 20° C.) and the 
beetles were exposed in wire-netting tubes (30 cm. long and 5 cm. in diameter). 
All geotropic reactions were tested in the dark, and if the animals crawled to 
the top of the tube when held in a vertical position they were considered positive, 
and if they moved to the bottom of the tube, negative. The phototropic reac- 
tions were tested with an ordinary 32 c. p. electric lamp in a constant-tempera- 
ture room. If the organisms crawled toward the direct rays of light when the 
tube was in a horizontal plane they were recorded as positive and if they moved 
away from the source of light as negative. 

ROLE OF WATER IN THE REPRODUCTIVE ACTIVITY. 

A striking fact that one observes in desert biology is that a remarkable degree 
of coincidence is shown between the rainy season and the reproductive period 
of the animals native to such a region. Corresponding periods of inactivity for 
such organisms occur during the dry season. In studying this problem. Tower 
(1906) finds this is true for most of the species of Leptinotarsa distributed 
over the American deserts and similar observations were made by Semper 
(1881) for several desert forms. 

For many years Tower has introduced chrysomelid beetles into desert com- 
plexes of Arizona from a wide range of habitats, and the majority of these 
experiments, which were placed under my care, showed that food, enemies, and 
the like were not the determining factors in the survival of such organisms, but 
that in most instances the survival was successful if the proper complex for the 
reproductive activity was attained. 

Frequent observations at Tucson indicated that the optimum breeding 
activity of the potato beetle was coincident with the highest water-content of the 
medium, since periods of egg-laying were exactly concurrent with those of rain 
and with the low rates of evaporation. Therefore, it was important to determine 
experimentally what relations existed between reproductive behavior and changes 
of water-content within the medium surrounding these animals. 

The literature of the subject contains much data in regard to the efi'ects of 
temperature upon the reproductive activity, but almost none upon the relation 
of water to reproduction. In reference to the genus Leptinotarsa, Tower (1906) 
states : 



The Potato Beetle in a Deseet 347 

" In both tropical and temperate latitudes, the germ-cells do not develop nor 
reproduction take place until the conditions of temperature and moisture are 

favorable Likewise, in the northern United States and Canada, decemli- 

neata may emerge from the ground in April, but the germ-cells do not begin to 
grow until the coming of the warm moist days in May or possibly June." 

Kammer's (1907) experiments show that Salamandra {maculosa and atra) 
can be induced in varying ways to lay their eggs, depending in part upon the 
moisture relation. Jacobs (1909) states for the rotifer PJiilodina rosela: 

" The period of maximum egg-production had been preceded by a period of 
desiccation and furthermore, that each desiccation for any length of time has 
been followed by an increase in the reproductive activity." 

Hennings (1907), working on the bark beetle Tomicus typographus Linn., 
finds that the amount of water present acted as a regulatory factor for such 
activities. The results of these investigators show that egg-production may be 
modified through changed water-relations. 

At Tucson Station A, comparative study of the environmental records indi- 
cated that when the atmosphere had a high water-content, and when the 
evaporation rates were low, then egg-laying took place most frequently. This 
was self-evident, for during the breeding of four generations of the stock at this 
locality egg-laying occurred during the following periods : July 7 to 19, August 
4 to 23, 1911 ; June 4 to 15, and July 15 to 29, 1912, which were exactly coinci- 
dent with the maximum rainy periods at this station. At Tucson Station B the 
results were similar to those of Station A, since the periods of oviposition were 
as follows : July 17 to 23, September 3 to 7, 1911 ; June 8 to 20 and July 24 to 
August 12, 1912, which coincided with high humidities and low rates of 
evaporation. At the Chicago station, however, the evaporation rates were lower 
and the egg-laying was controlled by other factors. For the desert complex 
these results indicated that the optimum for egg-laying was reached when the 
organism was subjected to a moist medium. 

Since these conclusions were only probable, it was advisable that they be sub- 
stantiated by further experiment. Therefore, it was necessary to produce 
artificial differences in the moisture-content of the mediima, and observe its 
effect upon beetles during hibernation and after emergence. 

For the purpose of these experiments, 120 beetles (Tucson A, g. II) were 
removed from hibernation at 8 p. m. June 19 and were placed in ground-glass 
stoppered weighing-bottles, so that no moisture could enter. They were removed 
immediately to the constant-temperature room of the Desert Laboratory, where 
reactions were tested and all responded positively to light and negatively to 
gravity. At the same time a sample of the soil surrounding the beetles was 
taken and found to contain 11.3 per cent of water by weight. The animals were 
now divided into two lots of 60 adults each (30 of each sex), which were found 
to weigh 10.007 grams and 9.845 grams, respectively. The first batch was sub- 
jected to differences in soil-moisture and its effect upon egg-production observed. 
In the second case the effect of changing evaporation-rates upon oviposition was 
also observed. 



348 



Eelation" of Watee to the Behavior of 



EXPERIMENTS WITH SOIL MOISTURE. 

It was important to determine the effect of a varying soil-moisture upon 
oviposition in these organisms during hibernation. Tubes used in experiments 
upon this subject were 30 cm. long and 15 cm. in diameter, and made of wire 
netting surrounded by several layers of tinfoil to prevent the egress and ingress 
of moisture. Three of these tubes were filled with a mixture consisting of equal 
parts of sand and adobe, and then sunk in a large box of sand, so that only the 
tops were exposed. The sand in the box was kept damp by means of self- 
watering automatic soil-cups, which were devised by Hawkins (1910), the 
purpose of this wet sand being to keep the organisms within the tubes at a 
uniform temperature, a result attained through rapid evaporation of water- 
vapor from the surface of the soil. 

The desired differences in soil-moisture were produced in the above tubes in 
the following manner: In one tube were placed two porous soil-cups, which 
gave the soil a high water-content; in the second one, however, a small porous 
soil-cup was placed, which kept the soil within at a lower moisture than in the 
former ; and in the third, no soil-cup was employed, thus keeping the soil dry. 
It was thus possible to obtain differences in soil moisture with other conditions 
approximately uniform. But to make certain that the above apparatus produced 
the desired results, determinations of soil-moisture within these tubes were 
made every second day throughout the experiment. These data are tabulated 
in Table 3, which shows that the moist soil contained 15.8 per cent moisture, 
the medium moist soil 8.8 per cent moisture, and the dry soil 1.9 per cent 
moisture. Thermometers were placed in these tubes at a depth of 15 cm. and 
readings were made at 5 and 9 a. m. and at 1, 5, and 9 p. m. When tabulated, 
these soil temperatures throughout the test indicated a close agreement for all 
experimental tubes. 

Table 3. 



Soil samples obtained. 


Tube 1. Moist soil. 


Tube 2. Medium 
moist soil. 


Tube 3. Dry soil. 


June 21 


Per cent. 
15.9 
15.6 
16.0 
15.8 


Per cent. 
8.9 
9.2 
8.4 
8.7 


Per cent. 
1.7 
2.1 
1.8 
2.0 




June 25 


June 27 • ■ 


Average 


15.8 


8.8 


1.9 



The 60 beetles of batch 1 were now divided into three groups, and when 
tested in the constant-temperature chamber were found to react positively to 
light and negatively to gravity. Each group was now weighed, group A weigh- 
ing 3.341 grams, group B, 3.329 grams, and group C, 3.337 grams, respectively. 
Each group was next buried on June 19 at a depth of 15 cm. in each of the three 
experimental tubes as indicated, members of A being buried in a moist tube, 
those of B in one less moist, and those of group C in a dry tube. These animals 
remained as buried until June 27, 6 p. m., when their weights were again tested 
in the constant-temperature room, and group A was found to weigh 3.213 grams, 
group B 2.962 grams, and group C 2.107 grams, respectively. 



The Potato Beetle in a Desert 349 

Thus it was discovered that the beetles of group A from the moist soil showed 
a loss of only 0.128 gram, while their reactions were, as before, positive to light 
and negative to gravity. The beetles of group B, however, from the medium 
moist soil, showed a much greater loss in weight (0.367 gram), although their 
responses were unchanged, except in the case of 3 which were positive to gravity. 
The beetles of group C from the dry soil indicated the greatest decrease in 
weight (1.123 grams), and showed a reversal in their behavior. 

After this test the beetles were put into separate cages out-of-doors and 
allowed to breed under natural conditions. A comparison of the rates of 
evaporation, obtained with Livingston atmometers when placed within these 
cages, indicated that the environment was uniform. When the activities of 
these insects were closely observed, the following results were obtained : Those 
beetles from the wet soil, whose reactions as previously tested, were still positive 
to light and negative to gravity, moved immediately upward on the potato 
plants, and began feeding on the uppermost leaves. This indicated that their 
activities were normal, and on June 30 eggs were laid. On the other hand, 
those animals from the medium-wet soil also fed on these plants, but no eggs 
were laid until July 4. This showed that oviposition was postponed 4 days, 
but that the dry-soil beetles, whose responses were now reversed, were negative 
to light and positive to gravity. They immediately burrowed into the ground 
and remained there until the arrival of the summer rains, July 13, when they 
emerged and laid eggs on July 15. In this case oviposition was delayed 15 days. 
An analysis of these results follows : 

These experiments showed that differences in soil-moisture produced changes 
in the water-content of these animals as well as modified their behavior. Since 
the egg-production was changed, we must conclude that beetles emerging from 
soils of high moisture-content lay their eggs sooner than those issuing from dry 
soils. The soil no doubt has played an important role in the economy of desert 
organisms, which are known to respond accurately to environmental changes 
such as we have described; otherwise many forms would have ceased to exist 
where they are now widely distributed in desert regions. 

EXPERIMENTS WITH EVAPORATION RATES. 

The second batch of beetles was used to determine the effect of differences 
in rates of evaporation upon insects just emerged from hibernation. The 
apparatus for this experiment consisted of three uniform bell-jars placed over 
pots of potato plants. Each pot was sunk into adobe soil in the bottom of a 
vivarium, which was an open inclosure covered with wire netting. One of the 
bell-jars was provided with 8 atmometers, which, through the evaporation of 
water-vapor from their surfaces, produced both a high relative humidity and a 
low rate of evaporation. The second jar was furnished with 2 atmometers, and 
the evaporation-rate was greater in this jar than in the first ; but the third was 
kept dry, for, since no water or atmometer whatsoever was used, a high rate of 
evaporation was secured. The food-plants in this test were kept in a normal 
healthy condition by the use of automatic soil-watering cups placed in the 
earth near the bottom of the pots. A few preliminary experiments demon- 
strated that the dry bell-jar in direct sunshine would become several degrees 
warmer than the more moist; consequently a shade was so placed as to give 



350 Eelation of Watee to the Behavioe of 

closer agreement in temperature readings. A small strip of wire-netting was 
then fastened around the base of each bell-jar to afford a free circulation of air. 

The environmental conditions produced artificially within each bell-jar were 
measured in the following manner : Thermometers were suspended in each jar 
and temperature readings were taken five times daily at 5 and 9 a. m., 1, 5, and 
9 p.m.; they show a close agreement of the three jars. The evaporation-rate 
was obtained by means of a single atmometer placed in each jar, and the cubic 
centimeters evaporated by this instrument were recorded twice each day at 8 a. m. 
and 8 p. m. In averaging the different rates, it was found that the moist jar 
showed an evaporation rate of 14.5 c. c. daily, the medium moist 20.7 c. c, and 
the dry 25.0 c. c, respectively. The results show that the air temperatures 
within each jar were approximately uniform during progress of the experiment, 
and furthermore that the anticipated differences in the rates of evaporation were 
produced in this manner. Thus the environmental conditions for this test were 
experimentally attained. 

Sixty beetles of batch 2 were now divided into three groups of 20 each, and 
on June 20 were distributed to the jars mentioned above. In the jar with a low 
rate of evaporation the beetles reacted normally in feeding upon the potato 
plants, and laid eggs on the third day, June 23, but in the jar with the medium 
evaporation-rate, the animals, though resting upon the plant leaves, laid no 
eggs for 9 days, or until June 29. In the third jar, with a high rate of evapora- 
tion, which produced the greatest degree of desiccation, they stayed upon the 
potato vines for 5 days or until June 25, when they entered the ground and 
there remained until the summer rains began July 11 ; they emerged, however, 
from the soil on July 13, and oviposition occurred within 3 days. 

These results showed that egg-production was modified by differences in the 
evaporating power of the air surrounding these animals, and that a low rate of 
evaporation, coincident with a high water-content, encouraged oviposition, but 
that a high rate of evaporation, which reduced their water-content, retarded 
reproduction. So with a high rate of evaporation the beetles were desiccated ; 
their tropisms were reversed and they entered the soil, where they remained 
until their moisture-content was sufficiently increased; they absorbed water 
until their reactions became normal, when emergence resulted. 

It was shown clearly that reproductive activity occurred during a period of 
high water-content in the surrounding medium, whether atmosphere or soil, 
and that desiccation, by reversing the animal's tropisms, inhibited and post- 
poned reproductive reactions of the L. decemlineata, which is a typical grassland 
organism. This demonstrated that the introduced stock had adjusted itself to 
the complex of desert conditions and reacted in the same manner as did the 
indigenous organisms of the surrounding region. Accordingly, in the majority 
of species, we should expect reproduction to coincide with the season of high 
water-content and a dormant period to follow the dry season, regardless of any 
discovered structural adaptations. 

ROLE OF WATER IN THE PRESERVATION OF LIFE. 

In the desert it was found that hibernating insects could continue life during 
long dry seasons of one or more years ; therefore, experiments were undertaken 
to answer the following questions : How was such vitality preserved ? Was this 



The Potato Beetle in a Desert 351 

relation due to a reduction of normal physiological activities through desicca- 
tion? If so, what relation exists between such organisms and changes in the 
physical composition and especially the moisture-content of the medium sur- 
rounding them ? For these tests, animals of different physiological activities, 
induced by differences in humidity, were buried for certain periods of time in 
soils of varying degrees of moisture and texture. The criteria used in deter- 
mining the power of resistance were the number of individuals surviving in 
the test at the end of a given period of time, and the differences in activities of 
the insects produced through desiccation, as compared to a similar set in which 
the behavior was normal. The capacity of these animals to resist was tested, 
and beetles were placed in wire-netting tubes (50 cm. long by 10 cm. in diam- 
eter) which permitted a free circulation of air and moisture. The tubes con- 
taining the insects were buried upright, so that the base of each was 60 cm, deep 
in the soil. The plots were 10 meters apart, in the open, at Tucson Station A. 
Earth was removed from each plot so as to leave two holes 6 meters square by 
1 meter deep, and each cavity was further divided into equal parts by a partition 
of red- wood boards 1 inch thick ; one side was filled in with sand, the other with 
adobe. One of these plots was exposed under natural conditions in the open, 
while the other was covered with a roof, which extended on each side 1 meter 
beyond the limits of the plot. This roof was raised 1.5 meters above the ground 
in order to give a free circulation of air and to keep the soil dry imderneath. 
Water from rains was collected in ditches which conveyed it beyond the plot. 
The plot in the open was designated Plot A, and that under roof as Plot B. 
The soils in both plots were kept moist by adding water by means of a garden 
hose until October 20, but after this date they were exposed to the conditions 
of the winter of 1911-12 at Tucson. 

The first set of experiments concerned only beetles of the summer generation 
that were emerging from the pupa state. Such insects do not normally hiber- 
nate, but may be caused to do so through adverse conditions such as those which 
cause desiccation. It should be noticed that in one instance the animals were 
buried with all activities normal; in the other, they were first induced to 
hibernate in cages in the vivarium, and they were sifted out in the soil; in 
either case they were finally buried under the conditions described above. 

In the former test in which the beetles were buried with all their activities 
normal, 400 emerging individuals (Tucson A, g. I) were collected on August 
12 ; 50 of these were then placed into each of the 8 wire-netting tubes ; 4 of these 
tubes were filled with sand and 4 with adobe soil; the insects were placed at 
corresponding levels in each of the 8 tubes ; 2 of these containing sand were 
buried in the open plot and 2 under the shelter, while the 4 tubes with adobe soil 
were sunk in the adobe sections of the plots, 2 in each. These were left unmo- 
lested until May 1, when one tube under each set of conditions was examined 
but no living beetles were found. On October 1, the remaining 4 tubes were 
inspected with the same results ; there were no living organisms found. These 
results showed that no beetles of the summer generation with their activities 
normal hibernated successfully when buried under the conditions of this experi- 
ment. These observations are tabulated in Table 4. 



352 



Relation" of Water to the Behavior of 



In the latter test, however, the insects were first induced to hibernate in 
cages in the vivarium, and were then immediately sifted out of the soil, to be 
finally buried in Plots A and B. The following methods were used in this test : 
During the period of August 13 to 20, emerging adults to the number of 1,613 
( Tucson A, g. I ) were collected and placed in pedigree cages under adverse con- 
ditions within the vivarium. These conditions were produced by having their 
food reduced to sliced potato tubers and by adding just enough water to keep 
the soil slightly moist, so that the beetles were partially desiccated. A census 
taken September 10 showed that 1,209 insects had successfully hibernated in 



Table 4. — Census of counts on covered plot and open plot. 






Conditions of the experiment. 


Covered plot. 




Open 


plot. 


Adobe. 


Sand. 


Adobe. 


Sand. 


a! 

> 

< 




44 
12 




48 
39 

49 
46 


T3 

ca 

0) 

Q 

50 
50 

6 

38 

50 
50 

2 
11 

1 
4 


> 














4 



a 
a> 

a 

50 
50 

50 
50 

50 
50 

50 
50 

46 
50 


> 

< 




46 





45 


47 



•a 
a 
v 

a 

50 
50 

4 
50 

50 
50 

5 

50 

3 
50 


> 

< 




4 





26 


39 



d 

V 

Q 

50 
50 

46 
50 

50 
50 

24 
50 

11 
50 


A. Beetles of summer generation: 

1. With activities normal when huried 
on August 12. On JMay 1 the fol- 
lowing count was made 


Another census on Oct. 1 showed.. . 

2. Others were desiccated and buried on 

Sept. 10. On May 1 the following 

count was made 

Another census on Oct. 1 showed.. . 

B. Beetles of winter generation: 

1. With activities normal when buried 
on Sept. 10. On May 1 the fol- 
lowing count was made 


Another census on Oct. 1 showed.. . 

2. Others were desiccated and buried on 

Oct. 2. On May 1 the following 

count was made 


Another census on Oct. 1 showed.. . 

3. Others were hibernated and buried on 

Oct. 7. On May 1 the following 


Another census on Oct. 1 showed.. . 



these cages, and from this result, it was discovered that their vitality was greatly 
diminished, for 67 per cent of them were killed by these conditions. Of the 
survivors, 400 were divided into 8 groups of 50 individuals each, which were 
placed in tubes buried beside the 8 which were described in the former test. All 
were left unmolested during the winter and until May 1, when 4 tubes from 
each plot were examined. Tubes from the covered plot showed that those in 
sand contained no life ; 2 from adobe contained 54 living beetles ; while 4 were 
alive in the sand from the covered plot; the adobe portion of this harbored 46 
living insects. On October 1 the remaining 4 tubes were also examined ; those 
in adobe soil imder shelter contained 12 living beetles, but all were dead in the 
sand and there were no living animals in either part of the open plot. These 
experiments proved that beetles of the summer generation, which normally 



The Potato Beetle in a Deseet 353 

breed and produce a hibernating winter generation, may be buried after having 
been induced to enter the ground through desiccation; furthermore, that the 
animals lived many months when buried under these conditions, but that the 
death-rate was greater in the sand, and the majority in the open plot succumbed. 
These data are also given in Table 4. 

On the other hand, the second set of experiments concerned beetles of the 
winter generation which had just emerged from the pupa state. This problem 
was considered from three aspects : (1) Some animals were buried with all their 
activities normal; (2) others were induced to hibernate through partial desicca- 
tion produced through adverse conditions, and were then buried; (3) many 
were allowed to hibernate normally before they were finally buried in the two 
plots. 

For the first test in which the animals were buried with all their activities 
normal, 400 emerging adults (Tucson A, g. II) were collected on September 10 ; 
they were placed within the sand and adobe portions of the two plots. During 
the winter, and until May 1, they were left unmolested, when tubes from each 
plot were examined and no living individuals were discovered. On October 1 
the remaining tubes were exhumed, but no live animals were found. These 
results showed that, when beetles of the winter generation, which normally . 
hibernate, were buried with all their activities normal, hibernation was unsuc- 
cessful and all the animals succumbed (Table 4) . 

In the second test, where beetles were induced to hibernate through desicca- 
tion, 1,000 emerging adults (Tucson A, g. II) were collected on September 11, 
and were placed under adverse conditions in pedigree cages in the vivarium, 
where their food was sliced potato, as in a previous test. On October 2, hiber- 
nating adults to the number of 692 were sifted from the soil, and 308 dead ones 
were gathered from its surface ; 400 of the living insects were then divided into 
8 groups, and were buried within the soils of the two plots, in order to afford 
the opportunity of winter hibernation. On May 1 these tubes were examined 
for living beetles ; the tube from sand under the covered plot contained no living 
adults, while in the one from adobe earth were foimd 48 living adults ; also those 
in sand from the open plot contained only 26 living individuals, while 45 beetles 
were removed from the tubes in adobe. In a similar manner, on October 1, the 
remaining 4 tubes were removed. In the adobe soil tube, under the shelter, 
were found 39 animals, but no individuals hibernated successfully in sand; 
moreover, tubes from the open plot harbored no life. The results indicate that 
induced hibernation was effected in the winter generation through desiccation, 
which increased the resistance of these animals by decreasing their normal 
activities. The only insects alive at the end of the experiment were found in 
adobe under the covered plot, which proved that potato beetles, when hiber- 
nating in adobe, possessed a greater resistance to desiccation than when buried 
in sand (Table 4). 

In the last test, insects were permitted to hibernate normally, then buried in 
Plots A and B. This was a control for former tests, since it showed that no 
error was introduced through handling or digging up the animals. For this 
test, 1,000 emerging adults (Tucson A, g. II) were collected on September 13; 
they were placed in a large out-of-door cage that was provided with potato 
plants, and other environmental conditions were apparently normal. After 
consuming much food, these animals were in hibernation by October 7 ; then, 
24 



354 Eelation" of Water to the Behavior of 

400 of these were sifted from the soil and buried in the adobe and sand portions 
of the two plots, after having been placed in tubes as in previous tests. On 
May 1, when 4 tubes from these plots were examined, it was found that the tube 
from adobe in the covered shelter showed 49 living beetles, while the one from 
sand contained only 4; on the other hand, the tube from the adobe portion of 
the open plot was found to have 47 living insects, and those from sand 39. On 
October 1, when the remaining 4 tubes were removed, those in adobe from the 
sheltered plot contained 46 live animals, but those in the sand none ; those from 
the open plot contained no individuals which had hibernated successfully. This 
natural type exhibited the greatest resistance because of the large number of 
survivals, and it also appeared that adobe was more favorable to the main- 
tenance of life than was sand. 

In Table 4 the results are briefly indicated; it is shown there that insects 
with all activities normal die when buried, for no beetles were found under any 
of these conditions. It appears also that either the summer or winter genera- 
tion may be buried and still live, providing the animals were desiccated previous 
to burial. It is also shown that a covered plot with adobe soil is a most favor- 
able condition for the preservation of life. It is also demonstrated that insects 
can be desiccated at any time, when they will burrow into the ground, and may 
remain there many months without apparent injury. These tests further show 
that the large pores in sand permitted too rapid drying, so that the animals were 
desiccated beyond recovery. Livingston (1910) shows that this adobe soil has 
a water-holding power twice as great as sand, which agrees with the above results 
and explains why these insects continued to live. Lastly, since the adobe soil in 
an arid region does contain such a high percentage of moisture, it therefore 
is the best medium for the sustentation of desert life. 

RELATION OF WATER LOSS IN INSECTS WHEN EXPOSED TO 
CHANGES IN THE RELATIVE HUMIDITY OF THE SUR- 
ROUNDING MEDIUM AND ITS EFFECT ON THE ACTIVITIES 
OF SUCH ORGANISMS. 

The relation of water-loss, i. e., transpiration and respiration from exposed 
surfaces, to the behavior of plants and animals has already received some atten- 
tion. This is especially true of plants, the water-relations of which have been 
studied by Livingston (1906), Lloyd (1912), MacDougal (1912), Renner 
(1910, 1911), and other plant physiologists. The results of Livingston (1906) 
are of interest in this connection, since they show that there is a close relation 
between the daily march of evaporation, as measured by the atmometer, and 
transpiration in plants. The following experiments upon insects show that 
these animals exhibit a physiological behavior not unlike that of transpiration 
in plants, but the results further show that tropisms of insects are modified by 
loss of water, which in turn is governed by the evaporating power of the air. 
There is wide literature upon perspiration, but it does not bear directly upon 
our problem ; accordingly we shall consider such researches as have been made 
upon transpiration and evaporation and the efficiency of these processes in 
modifying behavior. 

The results which follow upon the behavior of insects and other desert animals 
and upon the relation of evaporation to their behavior and life economy was 



The Potato Beetle in a Deseet 355 

reported, by the present writer (1911, 1912), and these results have been 
substantiated by Shelford (1914 a, h) and his students, Weese (1917), Hamil- 
ton (1917), and Chenoweth (1917). The writer's experiments upon the potato 
beetle and other desert animals (1911) showed that "the fundamental activi- 
ties of this beetle, as well as those of many desert organisms, are directly con- 
ditioned by their water-content or water-balance. The water-content of the 
beetle is determined by the evaporating capacity of the air, the leaf-moisture 
content of its food plant, soil-moisture, and temperature. Variation in any one 
of these factors may influence not only hibernation, but other habits and 
reactions." This work was carried on during the next year (1912), in which I 
stated regarding the behavior of desert animals that " the proportion of water 
held in the body, or the water-balance, is correlated with various activities, and 
the lowering of this balance, or surplus, inhibits several functions or processes, 
and is also followed by reversed response to various external agencies which may 
exert a stimulatory action." 

Shelford (1913) records that certain spiders, ground-beetles, wasps, milli- 
peds, frogs, and salamanders react in consequence of evaporation, and that a 
short exposure to evaporation conditions increases sensibility te it. Aside from 
this experimental data, Shelford and Deere (1913) established laboratory 
methods for determining the reactions of the above animals to evaporation 
gradients. My experiments differ from Shelford's in being made under natural 
conditions out-of-doors, while his studies were undertaken in the laboratory. 

Hamilton (1917) studied certain soil insects, in the full-grovm larval and 
adult state, of the family Carabidge, and his results tended to show that an 
increase in the rate of air-flow did not effect the larvas as much as did an 
increase in temperature or a decrease in relative humidity; the adults, more- 
over, offered greater resistance to evaporation and temperature. The experi- 
ments upon the horned lizard by Weese (1917) demonstrated a clear-cut reac- 
tion to the substratum temperature gradient, while the evaporation gradient 
was not the limiting factor. On the other hand, Chenoweth (1917) concludes 
that the evaporating power of the air is the best index of environmental con- 
ditions affecting the white-footed woodland mouse, as well as other land 
mammals, and that the mice reacted to evaporation whether it was produced 
by movement, dryness, or heat. 

EXPERIMENTS UPON EVAPORATION. TRANSPIRATION, AND BEHAVIOR. 

Previous experiments upon L. decemlineata show that tropic activities for 
light and gravity can be reversed through desiccation, and furthermore, that 
normal reactions are restored if the beetles were surrounded by a moist medium. 
On the other hand, it seemed important in this connection to perform certain 
experiments, in order to determine if these insects in nature react to losses of 
water, which might be produced through desiccation by means of the evaporating 
power of the air immediately surrounding them. Therefore, it seemed advisable 
to devise certain tests which would show the daily march of evaporation and 
transpiration when compared with their behavior. 

The first experiment was made to determine the relation between the daily 
progress of evaporation and transpiration rates of i^. decemlineata when exposed 
at three different strata, which were produced by an association of potato plants 
that completely filled the bottom of a cage, 6 feet square by 4 feet high, and 



356 Eelation" of Watek to the Behavior of 

covered with wire-netting. This dense growth produced horizontal zones with 
atmospherical moisture, varying from high water-content at the bottom of the 
cage to one of low content above the plants in the open. 

All beetle exposures and environmental measurements were made every 
2 hours for a period of 12 observations at 3 strata within the cage, where insects 
and instruments were exposed within wire-netting tubes, 30 cm. long and 
5 cm. in diameter. Stratum A was 5 cm. above the ground near the base of the 
potato plants, and contained the greatest moisture, thus giving the lowest 
evaporation rate; stratum B was 60 cm. above the ground, near the center of 
the cage among the plants, and was directly above stratum A, so that it con- 
tained less moisture, which gave a medium rate of evaporation ; while stratum 
C was 90 cm. above ground and 5 cm. above the tops of the plants, and furnished 
the driest conditions, with a high evaporation-rate, which was the only exposure 
to true desert conditions. Each stratum was directly above the other, and all 
exposures were made near the center of the cage. The environmental measure- 
ments were obtained as follows: The evaporation rates, by using Livingston 
atmometers ; relative humidities from wet and dry bulb readings ; temperatures, 
from uniform standard centigrade thermometers. 

The environmental measurements were made every 2 hours for a period of 
12 observations at the 3 strata within the experimental cage as previously 
described and at the beginning of each period a new batch of beetles was 
exposed to these conditions for 2 hours. The results are given in table 5. 

The beetles used in this experiment (Tucson A, g. II) were collected as soon 
as possible after their emergence. Since these newly emerged individuals take 
no food until after 24 hours, all collections were made previous to this time, so 
that no error might be introduced in consequence of feeding ; moreover, no food 
was given them at any time, and no excretion of waste products by the animals 
was observed throughout the test. The beetles were placed at once in bell-jars 
of uniform size in the constant-temperature room, which stood at 24° C, and 
a high but uniform relative humidity was produced by placing wet filter-paper 
inside the jars; this kept the air of the jars approximately saturated and the 
beetles absorbed moisture until their reactions and physiological states were 
uniform, as was proved by tests made later. 

The animals were retained in the jars until needed for further experiment. 
Three batches of 10 beetles were removed from the constant-temperature room, 
and exposed every 2 hours in wire-netting tubes, at the 3 strata within the cage. 
Each batch was made up of similar stocks as follows : 4 individuals of 180 adults 
which had emerged on July 5 were placed in the constant-temperature room at 
8 a. m. July 6; 3 adults of 110 individuals which had emerged on July 6 were 
also placed in this chamber on July 7 ; and 3 animals of 124 adults which had 
emerged on July 7 were likewise placed in this room at 10 a. m. July 8 ; while a 
batch of 30 beetles which emerged July 8 received the same treatment at 12 p. m. 
July 8, and were used during the last 2 hours of the experiment, beginning at 
4 p. m. on July 10. Thus all the organisms used were of the same culture and 
of the same parents ; in general they were of the same age, and approximately 
of similar states, so the conditions of the test were uniform. 

Aside from the environmental records, the following was also determined as 
far as the insects were concerned : the total weight in grams of 10 beetles when 
exposed, their weight in grams after 2 hours' exposure, the total grams of dry 



The Potato Beetle in a Desert 



357 



weight for each batch exposed, the grams of water in the beetles, the total per- 
centage of water in the animals, the loss percentage of water in terms of entire 
weight, and the loss percentage of water in terms of dry weight (Table 5) . 

















Tablf 


5. 














B 

_o 

1 

« 
o 

o 

6 


B 

3 


c 
o 

o 

« 

s- 

o 
<u 
et 

OS 


<u 
a 
"S 

V 

A 

i 

< 


•3 
S 

3 

«> 
> 


y 

It 

o o 

H a. 


« 3 

ll 

^ 2 

^§ 

El 


c 

'i 

•a 

£« 
P I. 

■- o 

►J 


Si m 

o " 


o 
K 
o g 

It 

o— ' 
H 


O . 


c 

"S 


o 

H 

■'- >. 








c. c. 


' c. 


p. ct. 


gms. 


gms. 


gms. 


gms. 


gms. 


p. Ct. 


p. ct. 


p. ct. 






fA 


2.0 


26.8 


36 


1.2957 


1.2700 


0.0257 


0.239 


1.0567 


81.55 


2.43 


10.75 


8 a. 


m.. 


iB 


2.3 


26.8 


33 


1.2879 


1.2574 


0.0305 


0.235 


1.0529 


81.75 


2.89 


12.98 






Ic 


3.6 


27.3 


30 


1.2367 


1.2028 


0.0339 


0.229 


1.0077 


81.48 


3.36 


14.80 






fA 


2.2 


27.9 


35 


1.2435 


1.2150 


0.0285 


0.230 


1.0135 


81.50 


2.81 


12.40 


10 a. 


ra.. 


\^ 


3.3 


33.2 


23 


1.2860 


1.2405 


0.0455 


0.275 


1.0105 


78.42 


4.50 


16.51 






Ic 


6.0 


33.9 


22 


1.2400 


1.1585 


0.0815 


0.226 


1.0135 


81.73 


8.04 


35.98 






fA 


2.7 


30.8 


35 


1.1840 


1.1496 


0.0344 


0.223 


0.9610 


81.16 


3.58 


15.42 


12 noon . 


.Jb 


4.6 


36.2 


19 


1.1740 


1.1196 


0.0.544 


0.213 


0.9610 


81.85 


5.66 


25.53 






Ic 


9.5 


36.2 


15 


1.1870 


1.0500 


0.1370 


0.218 


0.9690 


81.63 


14.14 


62.84 






fA 


4.3 


33.3 


30 


1.2090 


1 . 1320 


0.0770 


0.232 


0.9770 


80.81 


7.88 


33.19 


2 p. 


m.. 


.\b 


8.4 


40.2 


15 


1.2750 


1.1590 


0.1160 


0.272 


1.0030 


80.86 


11.56 


42.64 






Ic 


17.6 


40.0 


12 


1.2140 


1.0405 


0.1735 


0.236 


0.9780 


80.56 


17.74 


73.51 






fA 


4.6 


33.9 


28 


1.2415 


1.1610 


0.0800 


0.229 


1.0125 


81.55 


7.90 


34.93 


4 p. 


m.. 


.Jb 


8.9 


40.5 


13 


1.1005 


0.9805 


0.1200 


0.209 


0.8915 


81.00 


13.46 


57.41 






Ic 


19.4 


40.0 


11 


1.2540 


0.9800 


0.2740 


0.232 


1.0215 


81.46 


26.82 


117.84 






fA 


5.S 


28.3 


33 


1.2565 


1.2015 


0.0550 


0.215 


1.0415 


82.73 


5.28 


25.57 


6 p. 


m.. 


.Jb 


8.1 


37.3 


15 


1.2230 


1.1185 


0.1045 


0.213 


1.0100 


82.58 


10.34 


49.06 






Ic 


16.1 


37.1 


12 


1.1965 


1.0.550 


0.1415 


0.217 


0.9795 


81.86 


14.44 


65.20 






fA 


4.6 


28.4 


35 


1.20.30 


1.1815 


0.0215 


0.210 


0.9930 


82.54 


2.16 


10.24 


8 p. 


m.. 


. b 


7.6 


34.0 


19 


1.2.380 


1.1885 


0.0495 


0.219 


1.0190 


82.31 


4.85 


22.60 






Ic 


14.3 


33.4 


14 


1.2780 


1.2110 


0.0670 


0.234 


1.0440 


81.69 


6.41 


28.63 






r^ 


3.0 


25.4 


43 


1.2080 


1.1845 


0.0235 


0.213 


0.9945 


82.32 


2.36 


11.00 


10 p. 


m.. 


.Jb 


4.6 


30.6 


24 


1.1580 


1.1295 


0.0285 


0.214 


0.9435 


81.47 


3.02 


13.28 






Ic 


9.0 


30.0 


17 


1.2565 


1.2160 


0.0405 


0.239 


1.0175 


80.97 


3.98 


16.95 






fA 


2.0 


25.0 


44 


1.2660 


1.2375 


0.0285 


0.228 


1.0380 


81.99 


2.74 


12.50 


12 p. 


m.. 


.Jb 


3.1 


29.7 


27 


1.2230 


1.1900 


0.0330 


0.223 


1.0000 


81.76 


3.30 


14.79 






ic 


6.9 


29.0 


23 


1.2055 


1.1606 


0.0449 


0.220 


0.9855 


81.75 


4.55 


20.40 






fA 


2.1 


24.1 


47 


1.1727 


1 . 1420 


0.0307 


0.224 


0.9487 


80.89 


3.23 


13.70 


2 a. 


m.. 


.Jb 


3.2 


28.0 


31 


1.1693 


1.1380 


0.0313 


0.222 


0.9473 


80.01 


3.30 


14.09 






Ic 


6.7 


27.5 


27 


1.1384 


1.0489 


0.0489 


0.213 


0.9254 


81.29 


5.28 


22.91 






fA 


1.3 


24.3 


45 


1.1422 


1.1122 


0.0300 


0.224 


0.9182 


80.39 


3.26 


13.39 


4 a. 


m.. 


.Jb 


3.1 


27.1 


28 


1.2815 


1.2435 


0.0380 


0.251 


1.0305 


80.40 


3.68 


15.13 






Ic 


5.1 


27.2 


25 


1.1390 


1.0990 


0.0400 


0.225 


0.9140 


80.25 


4.37 


17.77 






fA 


1.2 


22.3 


56 


1.4385 


1.3975 


0.0410 


0.301 


1.1375 


79.07 


3.60 


13.62 


6 a 


m.. 


.Jb 


3.1 


25.2 


33 


1.4550 


1.4010 


0.0540 


0.312 


1.1430 


78.56 


4.72 


17.30 






Ic 


4.9 


25.2 


27 


1.5375 


1.4795 


0.0580 


0.328 


1.2095 


78.66 


4.79 


17.68 



358 



Eelation of Water to the Behavioe of 




8 10 12 2 4 
AM. P.M. 



6 8 10 12 2 4 6 
P.M. AM. 



Fig. 1. — -Curves showing relation between daily progress of evaporation and 
transpiration rates of beetles when exposed to different strata produced by an 
association of potato plants. Consult table 5 for above data. 



15 
14 
13 
12 
11 
10 
9 
8 
7 
6 
5 
4 
3 
2 
t 












1 










1 1 1 






















) 


Stratum 


C 






l."j 
14 
13 
12 
11 
10 
9 
8 
7 
iG 
5 
4 
'3 
2 




1 1 L 1 
Stratum A 














Stratum B 










/ 




Water Loss 
urve 2 = Rate of 

Evaporation 
urve 3 = AirTemp. 


Curve 1 = Rate of 

Water Loss - 
Curve 2= Rate of 










( 


rurve 1 = Transpiration Rate or 

Rate of Water Loss 
^urve 2= Evaporation Rate 


















( 














Evaporation" 
Curve3= Air Temp. 








































































































¥• 
































































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// 














































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/ 


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k — ^ 


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10 12 2 4 6 8 10 12 2 4 6 8 10 12 2 4 6 8 10 12 2 4 6 8 10 12 2 4 6 8 10 12 2 4 t 
VU. P.M. P.M. A.M. A.M. P.M. P.M. A.M. A.M. P.M. P.M. A.M. 





Fig. 2. — Results recorded in table 5 reduced to unity and curves plotted in 
order to draw a closer comparison than is given in figure 1. The same conclusions 
are self-evident. 



The Potato Beetle in a Desert 



359 



Figure 1 shows the plotted results for the data of this experiment. The broad, 
heavy lines give the results for stratum A, the broken line, the results at stratum 
B, and the narrow line those for stratum C. The abscissae represent the 2-hour 
time intervals, and each unit along the ordinate represents for the evaporation 
curves, 2.5 c. c. ; for the transpiration curves in terms of entire weight, 3 per 
cent; for the transpiration curves in terms of dry weight, 13,5 per cent; for the 
relative humidity curves, 5 per cent; and for the temperature curves 2.5° C. 
These graphs are interesting in that they show a close agreement between the 
evaporation-rate and transpiration curve for each stratum. Since the humidity 
and temperature curves coincide closely for the two upper strata, and the 
evaporation and transpiration curves for these strata vary in a similar direction, 
it appears that the rate of loss of water from the animals when exposed to the 
atmosphere agrees closely with the evaporation rates; i. e., the transpiration 
curves of these organisms, as Livingston (1906) found with plants, are largely 
controlled by the evaporating power of the air. 

Table 6. — Summary of rate of evaporation in each stratum combined with loss of 

water from the beetle. 



Location. 


Evaporation. 


Transpiration. 


Stratum. 


cm. 


c. c. 


Ratio. 


Loss per cent H^O. 


Ratio. 


A 
B 
C 


5 
60 
90 


35.3 

60.3 

119.1 


1.0 
1.7 
3.4 


47.2 

71.3 

113.9 


1.0 
1.5 
2.4 



Figure 2 shows the water-loss in percentage, the evaporation-rates, and the 
air-temperatures, all reduced to unity. The broad, unbroken line represents 
the rate of water-loss in each case ; the narrow, unbroken line, the evaporation 
rate for each stratum; and the broken line, the air-temperatures for each 
stratum. In making comparisons broadly, the air-temperatures agree in being 
represented by nearly straight lines, so that they were negligible ; but the 
evaporation curves and curves of water-loss differ for each stratum, yet are 
similar when compared. At stratum A, the evaporation curve rises more 
rapidly and higher than the curve of water-loss, and the drop in the evaporation 
curve is faster than in the curve of water-loss. At stratum B, the curves of 
evaporation and of water-loss parallel each other until 6 p. m, when the evapora- 
tion curve drops more suddenly. At stratum C the increased air-movement is 
an added factor in the environmental complex, so that both the water-loss and 
evaporation rates rise much higher, although the temperature curves remain 
the same. The curve of water-loss at stratum C rises more rapidly and higher 
than the evaporation curves. The latter drops sooner than the curve for 
evaporation. This appears to be due to the fact that the beetles are more 
sensitive to the environmental fluctuations than the porous-cup atmometer, so 
that difference might account for the lagging eif ect. 

These differences in the rate of evaporation in the three strata and the water- 
losses are given in Table 6, This table shows that approximately 1 c. c, loss 
from the cup is equal to 1 per cent loss of water from the beetles exposed. 



360 



Eelation" of Watee to the Behaviok of 



The evaporation rates here shown gave greater differences within this experi- 
mental cage than were obtained by Fuller (1911) for all the plant associations 
studied. Shelf ord (1912) uses Fuller's data with tables and compares them 
with conditions in certain animals, stating that distribution and succession of 
the animals is clearly correlated with evaporating power of air. By a further 
comparison with the description of stations, Shelford shows that the evaporating 
power of the air may be taken in this case as an index of materials, abode, 
and the like. Since the evaporation ratios existing inside of this cage 
filled with potato plants are greater than those obtained by Fuller for the 
stations such as Shelford used, it appeared that L. decemlineata reared in such 

Table 7. 



Environmen'tal conditions 
determined. 


Leptinotaria decemlineata subjected to desert conditions. 




15.2 


<K.2 


3 

01 


2 
E 

a 

Si 




"5 

'Z . 


c 

s 




c >. 
"" . 


c >. 

So . 




> 


CO 

> 

'S 
. 






Time. 


■a I, 


k. CO 

O ii 


Q. 

1 


4) 
> 

a >. 


o 

.a 

6 




•a S 
4,ja 

t Sf 




•a *: 

D tDJ3 


. no J3 

— S '* 

3 4/ S 
0— & 


6-2 




General Remarks. 




O 


X 


< 


a 


» 


w 


o 


a 





X 


z; 


CL, 








e. c. 


c. c. 


• c. 


% 


No. 


gms. 


gms. 


gms. 


%H^0 


%B„0 


No. 


% 






10 a. m. 


0.0 


0.0 30.2 


52 


25 


3.4650 


0.0000 


0.0000 


00.00 


00.00 


15 


60 






11 a. m. 


2.1 


2.131.4 


49 


25 












23 


92 






1 p. m. 


6.1 


3.134.0 


32 


25 












23 


92 






2 p. m. 


2.7 


2.7134.2 


33 


25 


3. '3270 


'.'1380 


'.'6345 


'islos 


"3 .'76 


15 


60 






3 p. m. 


3.1 


3.135.0 


32 


25 












21 


84 






4 p. m. 


3.9 


3.9 37.7 


32 


25 












21 


84 






5 p. m. 


3.2 


3.2 35.6 


33 


25 












25 


100 






6 p. m. 


4.3 


4.334.2 


31 


25 


3. '2365 


'.'6905 


';6226 


"9!86 


"2!47 


25 


100 






7 p. m. 


2.8 


2.832.3 


35 


25 












25 


100 






10 p. m. 


6.2 


1.7 


28.3 


46 


25 


3. '1870 


'!6495 


'!6i24 


"5!39 


"I'.Zh 


25 


100 






6 a. m. 


7.0 


0.9 


23.7 


77 


25 


3.1490 


.0380 


.0050 


4.14 


.52 


24 


96 






10 a. m. 


4.4 


1.1 


33.2 


49 


25 


3.0725 


.0765 


.0191 


8.33 


2.08 


24 


96 






2 p. m. 


14.8 


3.7 


22.5 


32 


25 


2.9895 


.0830 


.0208 


9.04 


2.26 


23 


92 






4 p. m. 


6.0 


3.0 


32.4 


42 


25 


















Very cloudy. 




5 p. m. 


0.0 


0.0 


22.8 


90 


25 


""{Bet 


ties in CI 


eased in weight.) 


11 


U 


Absorbed H^O 


from 


6 p. m. 


l.S 


l.S 


S6.8 


Ok 


25 


S.iZSO 


.4SS5 


.lies 


^7.22 


11.81 


SI 


8!, 


the air. 




9 p. m. 


3.0 


1.0 


25.2 


69 


25 


3.3940 


.0290 


.0097 


3.16 


1.05 


25 


100 






12 p. m. 


4.3 


1.4 


23.4 


73 


25 


3.3715 


.0225 


.0075 


2.45 


.82 


25 


100 






3 a. m. 


1.7 


0.6 


23.5 


70 


25 


3.3540 


.0175 


.0058 


1.91 


.64 


25 


100 






6 a. m. 


2.0 


0.7 


22.7 


82 


25 


3.3295 


.0246 


.0082 


2.67 


.89 


25 


100 






9 a. m. 


1.8 


0.6 


28.6 


66 


25 


3.2880 


.0415 


.0138 


4.52 


1.51 


23 


92 






12 a. m. 


6.4 


2.1 


31.4 


41 


25 


3.1825 


.1055 


.0352 


11.49 


3.83 


22 


88 






S p. m. 


9.7 


3.2 


33.6 


42 


25 


3.0840 


.0985 


.0328 


10.73 


3.58 


21 


84 


0.0705 gm. deducted for| 


6 p. m. 


6.7 


2.2 


31.2 


43 


23 


2.9405 


.0730 


.0243 


8.42 


2.81 


14 


61 


2 died. 




9 p. m. 


6.2 


2.1 


28.0 


52 


23 


2.9035 


.03/0 


.0123 


4.27 


1.42 


16 


70 






12 p. m. 


3.5 


1.2 


26.3 


62 


23 


2.8800 


.0235 


.0078 


2.71 


.90 


17 


74 






6 a. m. 


S.9 


0.7 


Zi.S 


72 


2S 


t.89S5 


.01S5 


(Beetles absorb H.O). 


78 


Absorbed H^O 


from 


6 p. m. 


IS.i 


1.1 


U.l 


9t 


is 


5.2695 


.S769 


.OSli 1 iS.ni S.6I1 iS 


100 


the air. 





a cage has a great range of adaptability. From the base of the potato plants to 
just a little above their tops, there existed zones of evaporation of wide extremes. 
To illustrate, Table 5 shows that from 2 to 4 p. m. at stratum A the evaporation- 
rate was 4.6 c. c. and loss in water-weight of beetles was 7.9 per cent of their 
entire weight; at stratum B the evaporation rate was 8.9 c. c. and loss of weight 
of animals exposed, 13.46 per cent; and at stratum C the rate was 19.4 c. c. and 
loss in weight of the beetles was 26.82 per cent. This shows the evaporation 
ratios to be 1.00: 1.93:4.22, and the transpiration ratios to be 1.0: 1.7:3.4. 
For the whole experiment, the ratios of evaporation were 1.0 : 1.7 : 3.4, while the 
transpiration ratios were 1.0 : 1.5 : 2.4. In general, these ratios are very similar, 
showing that there is a direct relation between the evaporation-rates and trans- 
piration percentages, and it answers in part the question already raised : Do 



The Potato Beetle in a Desert 



361 



the evaporation-rates, the transpiration curves, and the reaction graphs of these 
organisms correspond ? The following experiments give us a further affirmative 
response by showing that such a correspondence does exist in the potato-beetle 
and other insects. 

The first experiment was performed out-of-doors at the foot of Tumamoc hill 
near the experimental cages at Tucson Station A. The beetles which had 
newly emerged from the pupa state were collected at night. They were kept 
under saturated bell jars at a constant temperature until morning when they 
were placed in wire netting tubes. At 11 a. m. on July 19 they were exposed 
to the desert conditions in the open until 6 p. m. on July 21. The following 
environmental conditions were determined hourly : the rate of evaporation, the 




10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 2^ 



Fig. 3.— Curves 2 and 3 show the relation of evaporation to transpiration 
(water-loss) of beetles when exposed out-of-doors at the foot of Tumamoc hill; 
however, Curve 1 shows that the reactions of this insect to light were in general 
the reciprocal of the evaporation and transpiration curves. 



air temperature, and the relative humidity. During this experiment, the entire 
weight of the beetles was also determined, as well as periods when these insects 
gave off water to the atmosphere. It is of importance to plant and animal 
physiologists to state that these beetles absorbed water directly from the 
atmosphere. Aside from these determinations, others were made, which 
include the hourly loss in weight of these insects, the observed loss of water in 
terms of their dry weight, the daily loss of water in terms of dry weight, and 
the number of the beetles which were positive to light as well as the percentage 
positive to light. These results are given in Table 7 and the figures in italics in 
Table 7 show periods when the beetles absorbed water directly from the air. The 
evaporation rates and the transpiration and reaction rates of Leptinotarsa are 
plotted in figure 3. 



362 



Kelation of Water to the Behavior of 



By consulting this figure, one can see at a glance that the curves for trans- 
piration and evaporation correspond. Moreover, the reciprocal of the reaction 
or behavior curve also corresponds to these curves in a similar manner. Thus 
in the reaction of the potato beetle, its percentages of positiveness was, broadly 
speaking, the reciprocal of the transpiration curve. This seems to show that the 
loss of water from the animal, when exposed in the open, determined the reac- 
tions of the insect. 



Table 8. 



-Results of suhjecting other insects to the same environmental conditions 
as Leptinotarsa decemlineata. 



la- 
sects. 



Time, 



10 a. m. 

11 a. m. 

1 p. m. 

2 p. m. 

3 p. m. 

4 p. m. 

5 p. m. 

6 p. m. 

7 p. m. 
10 p. m. 

C a. m. 
10 a. m. 

10 a. m. 

11 a. m. 
1p.m. 

2 p. m. 

3 p. m. 

4 p. m. 

5 p. m. 

6 p. m. 

7 p. m. 
10 p. m. 

6 a. m. 
10 a. m. 

10 a. m. 

11 a. m. 

1 p. m. 

2 p. m. 

3 p. m. 

4 p. m. 

5 p. m. 

6 p. m. 

7 p. m. 
10 p. m. 

10 a. m. 

11 a. m. 

1 p. m. 

2 p. m. 

3 p. m. 

4 p. m. 
6 p. m. 

6 p. m. 

7 p. m. 
10 p. m. 



gms. 
7.2700 



6.7026 

6.4970 
6.3620 
6.1735 



1.5715 



1.0545 
0.8030 



2.9510 



1.9440 



1.3055 
1.2705 



> be 



gms. 
0.0000 



2055 
1350 
1885 

0000 



9 


5.1725 


9 




9 




9 


4.8263 


9 




9 




9 




9 


4.6005 


8 




8 


4.0340 



0575 
0290 

0000 
1665 

0880 

0380 
0360 



2258 
1590 



gms. 
0.0000 



0746 



0675 

0514 
0170 
0471 



0473 



0144 
0036 



0416 



0095 
0044 



0866 



0565 
0398 



•O <j 

His 



%H.O 
0.00 



10.34 

"y.'d'o 

5.19 
7.25 









22.16 



10.23 
7.30 



18.79 



9.84 
9.07 



27.54 



17.96 

u'.n 



0.00 



2.77 



2.59 

i!98 
0.65 
1.81 



2.56 
0.91 



4.70 



3.61 



2.46 
1.13 



4.49 
3.53 



No. 
9 

10 

10 

10 

10 

10 

10 

10 

10 

































mJ3 

C bl) 

1"^ 



p. ct. 

90 

100 

100 

100 

100 

100 

100 

100 

100 

































General Remarks. 



6 


56 


5 


66 


8 


89 


4 


44 


4 


44 


5 


56 


4 


44 


3 


33 















AU dead. 

3 dead ; deduct 0.235 gm. 

5 dead = 0.4595 gm. 
2 dead = 0.2225 gm. 
All dead. 

2 dead = 0.7525 gm. 
2 dead = 0.6005 gm. 
All dead. 



1 dead =0.4075 gm. 
All dead. 



The second experiment was performed to determine the relation of evapora- 
tion to the transpiration and reactions of insects when exposed for several days 
under natural conditions. To get a comparison between L. decemlineata and 
other insects, a cricket {Gryllus), a beetle {Catalpa lanigera), and two species 
of June-bugs (Lachnosternae) were used, since they could be collected in large 
numbers. These insects, with the exception of the potato-beetles, were obtained 



The Potato Beetle in a Deseet 



363 



at night by aid of a light, and were collected as soon as possible after emergence. 
All were placed at once in bell-jars in the constant-temperature room. A high 
relative humidity was produced as before by placing a wet filter-paper inside 
the jars, which permitted the animals, if not already saturated, to absorb water, 
so that their water-contents would be as uniform as possible, and they would 
attain, in this respect, a similar physiological equilibrium. The insects were 
retained under these conditions until 10 a. m. the following morning, when they 
were exposed in similar cylindrical tubes. The instruments for measuring 
environmental conditions were also placed in these tubes, which were suspended 
to a wire and placed in the open, so that each tube was inclined toward the north. 
The direct rays of the sun were thus permitted to fall upon the tubes at right 
angles. Unless otherwise indicated in Table 8, the observations were made 
hourly from 11 a. m. July 19 to 6 p. m. July 21, and for the environmental 
conditions consult Table 7. 



3.0% 

2.5% 



rt 2.0% 



1.5% 



1.0% 



^ 35= 



H 30° 



o 25' 



































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20" 

Hourly 
Units 12 3 4 5 



3.0?. 



2.5^0 



2.0% 



1.5% a; 



70? 



60^^ 



50t > 



40% < 



30% 



9 10 11 12 13 14 1 
Fig. 



5 16 17 IS 19 20 21 22 
4. 



23 24 25 26 27 28 29, 



If one should plot the results given in Table 8, he will find that all of the 
organisms used give a transpiration curve which corresponds with their curves 
of evaporation. Catalpa lanigera and the crickets reacted to transpiration in a 
manner not unlike the potato beetles, while the Lachnosternse always gave a 
negative response, regardless of conditions. 

Another experiment upon loss of water and insect activity was made as a 
conformatory test, in which the methods and materials used were similar. The 
animals consisted of 31 L. decemlineata (Tucson A, g. Ill), 10 Catalpa lani- 
gera, and 20 Lachnosternae. The latter were collected around an electric light 
and then placed in a refrigerator. All instruments and insects were exposed 
in the open in large netting spheres and hourly observations were made from 
9 p. m. August 9 to 4 p. m. August 11 ; the complete data are given in Table 9. 
The evaporation-rates, the air-temperatures, and the relative humidities are 



? 
■§ 

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The Potato Beetle in a Desert 



365 



shown in figure 4, while the transpiration and reaction curves of Leptinotarsa 
decemlineata and Catalpa lanigera are given in figure 5. The upper diagram 
contrasts for the potato beetle its transpiration rate with the percentage posi- 
tive to light, while the lower half of the cut does the same thing for Catalpa 
lanigera. This experiment was similar to the former ones, in that the insects 
were subjected to the environmental conditions out-of-doors at the foot of 
Tumamoc hill. 

For other data and comparisons Table 9 should be consulted; the results 
given show that the evaporation curve as measured by the porous-cup atmometer 
and the transpiration curves of the insects are similar, as was previously found 
to be true. Moreover, the positive reaction curve of the potato beetle was the 



55.0% 

•f 42.5% 

"I 
|30.0% 

II 

<>» 17.5% 

> 

6 

5.0% 

^ 8.21 

s 

I 6.2% 



^ 4.2% 



2.2% 

















1 


\ 


, 












1 






1 h 1 1 1 1 I 

Leptinotarsa decemlineata 


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Units 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 

Fig. 5. 



reciprocal of its transpiration curve. In the same way the reaction curve of 
C. lanigera was associated with its transpiration curve imtil 9 a. m., when all 
reactions became negative. The Lachnosternae appeared here only with a 
negative reaction, regardless of their transpiration curve, which agreed with 
the curve of evaporation. 

These results prove, in the first instance, that the evaporating power of the 
air was the determining factor in the transpiration of these animals, a result 
similar to that obtained by Livingston (1906) for plants; secondly, that there 
existed from the base to the top of associated plants, in an arid region, an 
extreme zonation, in which great differences were found in the evaporating 
power of the air, and that this in turn controlled the rate of transpiration ; and 
finally, that the evaporating power of the air surrounding the organisms deter- 
mined their behavior through transpiration. Moreover, many animal organisms 
of the desert exhibited great localization in their distribution and the ruling 
feature of the environmental complex, whether it entailed a habitat of trees, 
among rocks, or in soils, was that of the moisture-relation. 



366 Eelation of Water to the Behavioe of 

ROLE OF WATER IN HIBERNATION. 

It is an established fact (Tower, 1906) that in the second or winter genera- 
tion Leptinotarsa decemlineata in its homozygous state always hibernates under 
normal conditions, but that desiccation, or cold, or both, might produce hiber- 
nation at any time. At Tucson it was also found that whenever the conditions 
became adverse enough to produce desiccation, hibernation was produced. Tower 
(1906) showed that preparation for hibernation in the winter generation con- 
sists largely in the reduction of the watery contents of the body and in an 
elimination of all food and other substances from the alimentary canal. 

These facts indicated that the loss of water appeared to be produced by two 
different mechanisms. One was controlled by an external medium, while the 
other was determined by heredity. In the former, water was extracted from 
the tissues through desiccation due to conditions in the medium, while in the 
latter water was eliminated from the tissues through internal processes under 
normal conditions. Tower states : 

" Preparation for hibernation consists in a physiological change in the con- 
stitution of the body for the time being and a consequent lowering of the 
freezing-point of its tissues in exactly the same way that spores of many plants 
and the over-wintering eggs of rotifers prepare for the coming of the unfavor- 
able conditions in their environment." 

The following experiments were performed to show how the above results can 
be brought about through desiccation. At Tucson this type of hibernation was 
quite common, but did not occur in nature at Chicago. 

ENTRANCE INTO HIBERNATION. 

It is evident that in the potato beetle entrance into hibernation may be 
" induced hibernation," which occurred whenever the evaporating power of the 
air surrounding the insect removed more water by weight in a given time than 
was introduced into the organism by food and other agencies. Such desiccation 
produced in the course of one or two days depended upon the adversity of the 
conditions, thus effecting change in the beetle's behavior, so that its reactions 
were reversed and it burrowed in the soil. 

Extensive observations were made at Tucson Station A, where it was dis- 
covered that this type of hibernation took place whenever suflficiently desiccating 
conditions existed. The evidence of such a reaction in a large population was 
determined by comparing the daily environmental readings with counts of the 
non-hibernating population, which showed that during the rainy season and as 
long as water was added to the soil no entrance in this type was found, but when 
water was discontinued desiccation occurred and hibernation resulted. On the 
other hand, at Tucson Station B, the " induced hibernation " was always 
observed as the prevailing type of behavior, since in this habitat the conditions 
were more adverse. Moreover, at this locality, the growth of the food plants was 
retarded, since the leaves were tougher and showed less water-content; desicca- 
tion was also much greater, so that the response of the organisms to such 
rigorous conditions was sharper than in any other locality under observation. 
This clearly demonstrated when a comparison of the daily environmental 
records were made with the daily count of beetles, which were found out of the 



The Potato Beetle in a Deseet 367 

ground during one month of the rainy season. At Chicago, however, no induced 
entrance was discovered, since the conditions were more favorable there for 
normal activities, as the daily environmental readings indicate. From these 
observations it is evident that a type of hibernation occurred during periods 
of low water-content in the surrounding medium ; this produced a lowering of 
the beetles' content and induced a set of reactions so that a type of behavior, 
potentially hibernation, resulted ; to determine exactly the role of water-loss in 
the observed reactions other experimental tests were performed. 

For the purposes of this particular problem, the first test consisted of inducing 
aestivation by desiccating adults of the summer generation, which do not 
normally hibernate. The beetles for this experiment consisted of 259 adults 
(Tucson A, g. Ill) which had been placed in a culture cage filled with potato 
plants. They were allowed to feed until July 15, when a few bunches of eggs 
were deposited, and at 4 p. m. 200 of these beetles were collected and divided 
into two groups of 100 each, regardless of sex. The beetles were weighed, 
group A weighing 12.16 grams and group B 11.52 grams, respectively. Group 
A was now placed under a bell-jar with calcium chloride and group B under a 
similar jar filled with wet filter-paper. The jars with the beetles were placed 
side by side in an adobe building under identical conditions, except for differ- 
ences in the desiccating capacity of the medium within the bell-jars. Through- 
out the experiment the temperatures ranged from 26° to 38° C. At 8 p. m. 
July 24 these insects were removed from the soil in the bell-jar and reweighed. 
Group A from the desiccator weighed 8.53 grams, showing a loss of 3.63 grams, 
and group B from the humidor weighed 10.92 grams. Previously a box of soil 
(90 by 60 by 15 cm.) had been filled with a mixture of equal parts of sand and 
adobe, which also had been already saturated with water and was kept slightly 
moist throughout the experiment. Two bell-jars (a humidor and a desiccator) 
were placed side by side over the slightly moist soil in the above box ; insects of 
group A were placed in the latter, and those of group B in the former; after 
28 hours group A was in hibernation, but group B did not hibernate, although 
the beetles remained active upon the filter-paper. The calcium chloride was 
now removed from the bell-jar over the hibernated group A, and the soil was 
kept saturated ; at the end of 3 days 12 beetles emerged and after 6 days 57 more 
beetles were discovered, but at the end of 2 days no others had emerged; the 
soil was then sifted and 31 dead beetles were found. The individuals of group 
B still remained active, but none, however, had hibernated. These results 
show clearly that in the summer generation " induced " hibernation with a high 
death-rate may be produced through desiccation and, furthermore, that when 
water-balances were restored, all the living individuals emerged again and 
resumed the activities normal to their generation and season. 

To further substantiate the above conclusions other tests follow. In the 
fall generation, which hibernates normally, 1,000 newly emerged adults (Tucson 
A, g. IV) were collected on August 14, and divided equally, regardless of sex, 
into the following four groups: Each group was placed immediately in a 
separate wire-netting tube in the screened vivarium at Station A, and the tubes 
were made of wire-netting (95 cm. deep and 35 cm. in diameter), with a similar 
material covering the top. These were sunk 55 cm. into adobe soil composing 
the bottom of the vivarium, and each tube was filled to a depth of 53 cm. with a 
mixture of equal parts of sand and adobe. 



368 



Eelation" of Water to the Behavior of 



The following conditions were experimentally planned in tube 1, containing 
250 beetles, to give a low rate of evaporation, and the soil was kept moist by 
adding water each morning and evening. This tube was kept filled with sprays 
of Solanum hertwigii, which were kept fresh by having the stems in 250 c. c. 
bottles filled with water, and the sprays were renewed twice daily; it was also 
necessary to wrap tinfoil about the top of the bottles to prevent the beetles from 
drowning. The environmental conditions were apparently normal, for the 













Table 


10. 






















Tube 1. 


1 


Tube 2. 


Tube S. 


Tube 4. 


When observed. 


Food and moist. 


Food and dry. 


No food and dry. 


No food but moiat. 


6 

Q. 

a 




S^ 


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6 
0. 


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55 


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c. c. 


August 14, 6 p. m. 
15,6 a. m. 


Set 
1.2 


250 








Set 
6.0 


250 








Set 
6.9 


250 








Set 
1.8 


250 








6 p. m. 
16,6 a. m. 


4.3 








21.2 








22.7 








6.4 








2.0 








4.3 








5.9 








2.8 








6 p. m- 
17,6 a. m. 


6.1 


250 


6 





22.0 


249 





i 


23.7 


24i 


"0 


9 


8.2 


250 


6 


6 


1.0 








4.1 








4.9 








1.8 








6 p. m. 


5.7 








21.2 








24.7 








7.3 








18, 6 a. m. 


1.1 








5.0 








5.9 








1.8 








6 p. m. 
19,6 a. m. 


6.2 


250 


6 


6 


19.1 


241 


7 


'2 


21.8 


231 


"'9 


"io 


8.2 


248 





'2 


2.1 








6.3 








6.7 








2.8 








6 p. m. 


6.4 








22.2 








22.7 






_ 


9.2 








20,6 a. m. 


4.0 








7.0 








6.9 








5.5 








6 p. m. 
21,6 a. m. 


6.8 


248 





2 


26.9 


124 


86 


'4! 


23.7 


isi 


ig 


"74 


8.2 


243 





ii 


2.2 








6.3 








5.9 








3.7 








6 p. m. 
22,6 a. m. 


5.9 








25.2 








24.7 








8.2 








2.1 








5.2 








5.0 








3.7 








6 p. ra. 
23, 6 a. m. 


4.6 


245 


6 


5 


21.3 


53 


12! 


'76 


21.7 


i33 


38 


'79 


7.3 


236 


6 


14 


3.0 








4.6 








5.0 








4.6 








6 p. m. 


7.1 








18.3 








20.7 








9.2 








24,6 a. m. 


4.9 








6.3 








5.9 








5.5 








6 p. m. 
25, 6 a. m. 


!6.1 


24 i 





9 


24.6 


"6 


i57 


93 


19.8 


104 


'57 


89 


7.3 


22 i 





29 


4.0 








5.3 








5.0 








5.5 








6 p. m. 
26, 6 a. m. 


5.6 








24.2 








21.7 








7.3 








4.1 








6.1 








5.9 








5.5 








6 p. m. 
27, 6 a. m. 


7.0 








23.8 








22.8 








8.2 








2.0 








6.0 








6.7 








3.7 








6 p. ra. 
30,8 a. m. 


3.2 


222 


6 


28 


18.2 


"o 


157 


93 


23.0 


"0 


i29 


i2i 


1.5 


177 





73 


Tubes r 


emoved, soil sifted, and all hibernated 


adults found 






to be alive. 





water-condition, the food-supply, the low rate of evaporation, and the soil- 
moisture were all favorable for the normal activities of the animals used (Table 
10 for tube 1) in this problem. 

The following set of experimental conditions was maintained in tube 2, which 
contained 250 beetles; however, in this case the soil was kept only slightly 
moist and the first 5 cm. was used as a dry mulch, so that less moisture was lost 
through evaporation. The same food plants, Solanum hertwigii, were added 



The Potato Beetle in a Desert 369 

thrice daily, but only a few small sprays were used each time, so that the air 
within the tube was free from dampness, a condition which would have increased 
the evaporation rate and assisted in making the environmental situation un- 
favorable. The environmental conditions in this case were normal, in so far as 
the food-supply was a factor; but the other surroundings were modified, at 
least as to the high rate of evaporation (Table 10 for tube 2) . Both tubes 1 and 
2 were planned to give the ascertained differences in evaporation-rates ; accord- 
ingly tube 1 produced a lower and tube 2 a higher rate, but the food relations 
for both were approximately normal. 

No plants were used in tubes 3 and 4, but each tube was wrapped with several 
thicknesses of coarse absorbent paper ; at the beginning of the test the soil within 
each was saturated with water, but no water was added during the experiment. 
Around the outside of tube 4 was placed a coil of lead-tubing drilled full of 
holes, and this was connected to a carboy of water. This device kept the 
absorbent paper surrounding the tube saturated and, furthermore, a large piece 
of oil-cloth was wrapped to the height of 15 cm. around the base of the tube 
and beneath the absorbent paper. This oil-cloth was extended out in all direc- 
tions for about 60 cm. from the bottom of the cage, so that the dripping water 
did not come in direct contact with the soil in the tube. On the other hand, no 
water was added to tube 3, so that this cage was kept dry during the experiment. 
These conditions, therefore, produced a high rate of evaporation in tube 4 and a 
low one in tube 3 (Table 10) . The results for each of these tests follow. 

The 1,000 beetles used in this experiment were grown under the same environ- 
mental conditions and from the same parents, and, moreover, these animals had 
emerged as adults from the pupa state synchronously; so they were then as 
nearly uniform physiologically as it was possible to obtain them. The con- 
clusions showed for tube 1 with plenty of food and moisture, when the indi- 
viduals were counted at the end of the experiment, that there was no hiberna- 
tion ; 28 were found dead upon the soil. In tube 2, with plenty of food, but in 
which the air was kept dry, the census, when taken at the end of the test, showed 
that 157 had successfully hibernated and that 93 had died. At the end of the 
experiment tube 3, which contained dry air and no food plants, showed 129 
beetles in hibernation and 121 dead ones. Tube 4, which was supplied with 
moisture but with no food, at the end of the test gave no evidence of hibernation ; 
73 of the 250 beetles originally present were found dead upon the soil. These 
results proved that newly emerged adults of the fall generation can not be 
caused to hibernate under normal conditions, but that if the surrounding 
medium was dry a type of hibernation reaction did result through desiccation. 
Such deductions are possible, since the evaporation rates in Table 10 show that 
a low rate retarded hibernation and a high one accelerated this behavior. 

It is also true that this entrance into hibernation may be of the normal type, 
which always occurs under normal conditions in the winter generation. Low 
temperature, however, was an important factor at Chicago, but this kind of 
hibernation also took place in the pure winter-generation stock, even under high 
temperatures. This behavior was further studied in the second generation of 
the year under the following set of experimental conditions. 

At Tucson Station A this type of hibernation reaction in beetles of the winter 
generation (Tucson A, g. II) was observed to appear under a normal environ- 
mental complex in the fall of 1911, but all other hibernations (Tucson A, g. IV), 
25 



370 Eelation of Wateb to the Behaviok of 

which took place "imder adverse circumstances in the early fall of 1912, were of 
the induced type. At Tucson Station B this behavior was not discovered in 
either the winter generation of 1911 or that of 1912, since the environmental 
conditions always produced desiccation in the early fall at this locality, thus 
causing the beetles to be in hibernation about 10 months each year ; they emerged 
about the middle of July, and after feeding for a short period re-entered hiber- 
nation late in August. At the Chicago Station, however, normal hibernation 
always occurred, because the environment was normal, for no excessive desicca- 
tion or any other climatic adversities appeared. It became necessary, therefore, 
to determine if these results could be confirmed by further data, so the following 
hibernation tests were carried out. 

For these tests 30 emerging adults (Tucson A, g. II) on September 2 were 
placed in a hibernating pedigree-cage containing potato plants for food; the 
soil was a mixture of equal parts of sand and adobe, and water was added twice 
daily, but the plants completely filled the cage. The experimental conditions, 
therefore, were apparently normal throughout the test. It was discovered by 
daily observations that these animals were in hibernation on September 18 and 
when dug up on October 2, the first adults were uncovered at a depth of 20 cm., 
but the larger number of beetles were found at the bottom of the pot. The 
beetles were inactive when first removed, but began to move in a few minutes at 
an air-temperature of 33° C. Various tests in the field demonstrated that they 
possessed no reactions to food or dry soil, but within 5 minutes they did respond, 
and all burrowed into the moist earth at a temperature of 21° C. This indicated 
that a cool moist soil accelerated the entrance reaction. These results were 
further tested to determine if similar reactions always took place. 

On September 2, 130 emerging adults (Tucson A, g. II) were put into a 
hibernating cage, which had been previously filled with potato plants, and in 
which the soil consisted of a mixture of equal parts of adobe and sand, to which 
water was added twice daily; thus the conditions were approximately normal, 
for no desiccation occurred. The beetles responded to this set of conditions, 
for they were in hibernation by September 22. When dug up on October 21 
the insects were found distributed through the soil from the top to the bottom 
of the cage, but when tested in the field showed no reaction to food or dry soil, 
and when brought into contact with cool moist soil, out-of-doors, they burrowed 
into it within 5 minutes. 

This activity was again tested in the following manner: 51 emerging adults 
(Tucson A, g. II) were removed September 3 and were placed in a hibernating 
cage filled with Solanum hertwigii for food. In this experiment a different 
food plant was also used, but with no apparent result upon their behavior. The 
soil was also of equal parts of sand and adobe, and water was added each morning 
and evening, so that the experimental conditions were apparently normal. All 
the animals were in hibernation by September 19, but when dug up on October 3 
only 46 adults were alive. The first individuals, however, were discovered at 
a depth of 29 cm., and the majority were at the bottom of the pot. When 
tested in the field no reactions to food or dry soil were observed, but when 
brought into direct contact with cool moist earth all burrowed into it imme- 
diately. Thus when normally hibernating beetles of the winter generation were 
removed from hibernation a cool moist soil was necessary to initiate this 
behavior. 



The Potato Beetle in a Desert 



371 



ACTIVITIES DURING HIBERNATION. 

It was observed that hibernating beetles were inactive when first dug from the 
soil, and if the insects were moved to a warm room they soon began to crawl ; 
then entrance into hibernation occurred if they were brought into contact with 
moist earth. At Chicago, during the winter of 1911-12, it was observed that 
beetles which had hibernated out-of-doors migrated more deeply than usual 
during the cold winter. From the following test it appeared that beetles would 
move to moist regions in the earth during hibernation, for late in April 1912, 
at Tucson Station A, several hundred individuals were found to be hibernating 
in the open air cage. Accordingly a corner of this cage was watered and the 
soil was sifted ; thus, all the beetles were removed in that locality, but the newly 
dug soil was kept moist, and each week it was examined for adults ; during each 
observation a large number was always discovered. 

WATER RELATION OF SOILS AND HIBERNATING BEETLES. 

The beetles hibernate in small cavities or cells, which contain air of a relative 
humidity, that is in proportion to the water-content of the surrounding earth. 
During heavy rains the soil becomes flooded with water, so that some air is 
driven from the cavities, but if the rain continues for too long a period the 
beetles may die. On the other hand, if the soil is too dry, desiccation of the 
insects takes place and death may result ; therefore, the part soil-moisture plays 
in mortality during hibernation is of great significance. Tower (1906), in 
discussing results with soils, states: 

" The water-content of soil is controlled, not by an abundant rainfall, nor by 
telluric water, but almost wholly by adhesion and capillarity in the soil — that 
is, physical conditions alone, such as permeability, capillarity, and the power to 
absorb and to retain water are the factors which influence the moisture content 
of soil .... In all soils the pores which do not contain water are filled with air 
in which the percentage of relative humidity is controlled by the amount of 
water in neighboring pores. Likewise, the cells in which these beetles pupate 
are filled with air ; the relative humidity is controlled by water in the pores of 
the surrounding earth." 

Thus the physical composition of the soil is important in preserving insect 
life, and the adobe soil of the Tucson Desert, although it contains but little 
moisture, does possess other physical potentialities which act in retaining 
moisture, for through drying it becomes impervious to water and hibernating 
animals are sealed up in their cells and thus preserved from desiccation. To 
determine how dry the adobe soil was when containing living beetles, samples 
of it were taken from the walls of the cells (Table 11) and those of June 30 

Table 11. 



Date. 


Depth. 


Wet soil. 


Dried soil. 


Water-lo88. 


Water-content. 


April 1 

April 8 

April 30 

June 30 


cm. 
25 
25 
25 
5 
10 
20 


ffms. 
60.93 
122.22 
123.84 
58.94 
76.55 
58.09 


gms. 
56.18 
110.00 
115.89 
57.64 
73.55 
55.45 


gms. HjO. 
4.75 
12.22 
7.95 
1.30 
3.00 
2.54 


per cent HjO. 
8.45 
11.11 
6.85 
2.25 
4.07 
4.45 



372 Eelation" of Watek to the Behavior of 

showed an average of less than 4 per cent water of their dry weights. This 
was during the dry season, when no beetles had emerged from hibernation up 
to the above date, but on July 1, the day following, 0.98 inch of rain fell; 73 
beetles emerged on July 3, and by July 3 eggs were laid. This sharp response in 
behavior must be attributed to the water-content of the soil, for the beetles 
emerged immediately after the first rain and oviposition took place within 
48 hours. The insects of the surrounding desert showed a similar response, 
inasmuch as the adobe soil held them imprisoned until the first rain, which 
raised their water-content and softened the soil so that emergence of immense 
numbers occurred. 

The following experiment was performed to show the relation of physical 
composition of soils to mortality during hibernation. Three hibernating cages 
were prepared containing soils, one was composed of sand, another of adobe, and 
a third of equal parts of sand and adobe. On October 1, 500 hibernating adults 
were caused to hibernate artificially in each tube by placing the insects at a 
depth of 40 cm. in the soil, and the soil within each tube was kept slightly moist 
until late in October; they were then allowed to remain out-of-doors under 
natural conditions during the winter until May 1, when water was added to each 
cage. On May 3, 363 adults emerged from the soil mixture, 251 from the adobe, 
but none from the sand. On May 5, the soil of each cage was sifted, when it 
was found that all in the pure sand were dead but that only 27 in the adobe 
and 23 in the soil mixture had succumbed. It appeared, then, that there was a 
relation between soil composition and mortality during hibernation, for the 
sand permitted excessive desiccation to occur, the adobe and mixed soils did 
not admit of great desiccation, but most individuals were hibernated suc- 
cessfully in the mixture of equal parts of adobe and sand. 

EMERGENCE FROM HIBERNATION. 

The physiological complex of emerging beetles was next considered in refer- 
ence to two phases of the problem. In one case the reactions of hibernating 
beetles caused to emerge by applying water to the soil were determined, and in 
the other the reactions of similar adults, in which emergence was produced by 
sifting the soil, were tested. In the first experiment hibernating beetles (Tucson 
A, g. II) were encouraged to emerge by applying water on June 1, when they 
were removed to the constant-temperature room ; their reactions were found to 
be positive to light, but negative to gravity. The light response was further 
tested by placing 5 beetles in each of 10 test-tubes and each tube was placed so 
that one-half of it was in the shade of the laboratory roof and the other half 
in direct sunlight. The beetles all oriented and moved out into the sunlight 
at the end of each tube, where they remained, and in a few minutes were dead. 
The air-temperature in the exposed ends of the tubes was 57° C. In this experi- 
ment the organisms reacted to sunlight and the suggestion that possibly the red 
or blue rays might have influenced this result led to the next test. 

Of 50 hibernating individuals (Tucson A, g. II) emerged after adding water 
on June 3, 25 were put in each of two test-tubes; one of which was placed in 
direct sunlight under a red bell-jar containing a potassium-bichromate solution, 
and, while no deaths occurred, no definite reaction was observed ; the other was 
placed in the direct sunlight beside the former, under a blue bell-jar provided 
with a solution of copper sulphate, when all became positive to the rays and 



The Potato Beetle in a Deseet 373 

none died. We may therefore conclude that death in the first experiment was 
due to heat. 

Many tests of various kinds have been given elsewhere and with the same 
result — that when hibernating beetles were caused to emerge by applying water, 
they reacted positively to light and negatively to gravity. The next experiment 
consisted in testing the reactions of hibernating beetles, in which emergence 
was attained by digging and no water was added to the cage. 

For this test 47 hibernating beetles (Tucson A, g. II) were removed by 
digging at 8 p. m. on June 12. They were negative to a 32 c. p. lamp, but 23 of 
these insects were positive to candle-light of a weak intensity. These were 
immediately placed under a bell-jar containing moist filter paper, and when 
tested on June 13 they were found to be positive to light but negative to gravity. 
This behavior was repeated in the following case. 

Twelve hibernating beetles (Tucson A, g. II), when removed by digging at 
7 p. m. on June 20, were found to weigh 1.2573 grams, but they gave no response 
to light or gravity. (A soil-sample taken from the earth surrounding the beetles 
showed that it contained water to the extent of 12.7 per cent of dry weight.) 
When the animals were placed in a humidor at 10 a. m, on June 22, they 
weighed 1.3057 grams, having absorbed 0.1484 gram of water from the moist 
chamber; 10 of these beetles, when tested, were positive to light, but 2, which 
were inactive, died in a very short time after the experiment. The 10 adults 
were also negative to gravity, for when placed in the constant-temperature dark- 
room, all crawled to the top of the cylindrical wire-netting tube. These experi- 
ments showed that positive phototropic and negative geotropic reactions were 
induced in hibernating beetles by increasing the water-content of the surround- 
ing medium, because the beetles under the moist bell- jar increased in weight and 
imbibed water directly from the moist air. It was also true that they absorbed 
water from the air in the soil. This relation was further shown in the following 
observations, which were made upon the emergence response. 

The time of emergence is controlled by the environmental complex, for if 
water were added to the medium surrounding hibernating beetles, when the soil 
temperatures were above 14° to 16° C, emergence resulted. This was evident 
at Tucson, for no emergence was discovered at either station until the rainy 
season in July, and furthermore, the winter rainy season caused no emergence 
because of low temperatures. At Chicago, emergence occurred whenever the 
soil-temperatures reached 14° to 16° C, for enough precipitation always took 
place during the winter and spring months so that emergence occurred as soon 
as the proper temperature relations existed, which was from May 20 to June 25. 

SUMMARY AND DISCUSSION UPON THE RELATION OF WATER 
TO HIBERNATION. 

The conclusions arrived at from these previous results indicated that a type 
of liibernation might be produced at any time through desiccation, except with 
low temperatures, when little desiccation took place. This condition produced 
a loss of water from the beetles in such a way that they responded negatively to 
light and positively to gravity, so that they burrowed into the soil and remained 
there until the moisture-content of the soil was sufficiently high. They then 
absorbed hydroscopic water, which raised their water-content and reversed their 
reactions, so that they became positive to light and negative to gravity, hence 



374 Relation of Water to the Behavioe of 

their emergence, so that now, in case other conditions were suitable, they were 
ready to enter upon their reproductive activities. Below 12° to 15° C. in soil- 
temperature the water-relation was not the controlling factor, but the duration 
of the hibernating period depended upon the length of the dry season in an arid 
complex and upon the length of winter (low temperature) in a temperate 
region. 

Baumberger (1914) reviews, at length, the literature on hibernation of insects 
and reaches the following conclusions, chiefly from his own researches : 

" 1. That temperature is but a single factor and not necessarily the con- 
trolling one in hibernation. 

" 2. That hibernation is usually concomitant with overfeeding and may be 
the result of that condition or the result of accumulation of inactive substances 
in the cytoplasm of the cell due to feeding on innutritive food. 

" 3. That the loss of water which is general in hibernation probably results 
in a discharge of insoluable alveolar cytoplasmic structures which have accumu- 
lated and produced premature senility with an accompanying lowering the rate 
of metabolic processes. 

"4. That starvation during hibernation, together with loss of water, may 
result in rejuvenation, when aided by histolysis, and an increase in permeability. 

" 5. That this rejuvenated condition and increased permeability will, if 
stimulated to activity by heat, permit pupation in codling-moth larvas, which 
in this case is the termination of the hibernating conditions." 

The results of Sanderson and Peairs (1913) add another condition for 
hibernation that was also discovered by Tower (1906) for the potato-beetle; 
this is the influence of heredity. The former authors reached the following 
conclusions : 

" That our first work was an efl'ort to show that emergence from hibernation 
was due to an accumulation of temperature, but it soon became apparent that 
hibernation is very largely controlled by the influence of heredity, and that the 
relation of the temperature and inheritance must be determined for each 
species." 

For the Mexican cotton boll weevil, Hunter and Hinds (1904) found that 
dryness was more desirable for hibernation and that mortality during hiberna- 
tion was greater from exposure to moisture than from cold; but, on the other 
hand, high temperatures and moisture were the best conditions for the develop- 
ment of such beetle larvae. In this connection, Baumberger (1914) stated: 

" The effects of ether on plants is similar to hibernation and since the action 
of ether is probably a drying one, this may throw light on the importance of 
moisture in hibernation." 

Loeb (1906) says: 

" The lack of water acts similarly to a low temperature. This is the reason 
why seeds can be kept alive so long. Lack of water may reduce the reaction 
velocity of the hydrolytic processes in seeds at ordinary temperature so con- 
siderably that it may become practically zero." 

The snail, according to the results of Kiihn (1914) loses weight in winter 
and reacts to drought in summer. Unless it contains a large amount of water, 
no dry food is taken, and if placed under moist conditions when in hibernation 
it will come out of its closed shell. Bellion (1909) finds that a low moisture- 
content of the air is the determining hibernating factor in the European snail, 



The Potato Beetle in a Deseet 375 

and Baker (1911) shows that snails during dry seasons form an epiphragm ; 
they usually bury themselves during hibernation and aestivation. On the other 
hand, Pearl (1901) finds that the terrestrial slug Agriolimax can hibernate in 
cold water. 

In the vertebrates, Rulot (1901) determines for the bat that the proportion 
of water increases during hibernation from November to April; but there 
actually was a loss of water, more in proportion at the end than at the beginning. 
Polimanti (1904) finds that an increase in humidity increases the pounds in a 
marmot during hibernation. 

In conclusion, the work of Sanderson (1908) agrees most closely with my 
results upon hibernation. In discussing the relation of temperature to the 
hibernation of insects, he states : 

'' In come cases, however, the time of emergence from hibernation is con- 
trolled by moisture conditions as well as temperature, or independent of tem- 
perature. Thus Tower kept the potato beetle in hibernation for 18 months at a 
high temperature but with a dry atmosphere, and they emerged as soon as 
normal moisture conditions were produced. Webster and Hopkins have shovni 
a similar effect of the lack of rainfall on the emergence of the Hessian fly in the 
fall. In relation to hibernation in humid climates the matter of moisture is 
probably not a controlling factor, but undoubtedly has the most important 
influence upon the time of emergence of forms in aestivation during the summer 
or in an arid region." 

My results upon the potato-beetle substantiate the work of Sanderson. 

EFFECT OF CHANGES IN WATER-CONTENT UPON ALTERATIONS 
IN TROPIC ACTIVITIES. 

The experiments and observations upon L. decemlineata proved that, when 
surrounded by a moist medium, the beetles were positive to light and negative 
to gravity. It is also evident from previous tests that if the moisture of the 
surrounding medium was decreased, desiccation resulted, so that the insects 
were reversed in their behavior and reacted negatively to light and positively to 
gravity. These beetles, however, responded to any intensity of light if moved 
from a lesser to a greater intensity, and accordingly when moved from darkness 
into the moonlight at Tucson they always reacted ; and in many instances insects 
which were negative to a strong light were also positive to a weak one. 

It was shown by Burdin (1913) that heat and dryness stimulate positive 
reactions in terrestrial amphipods, while cold, moisture, and quiet favor nega- 
tive reactions. The results of Dice (1914) prove that light of high intensity 
makes daphnias positively geotropic, but a decrease in light intensity has the 
reverse effect; and furthermore, these animals tend to become positively 
geotropic in high temperatures and negatively geotropic in low. Kanda 
(1916a), in studying geotropism in a marine snail, found that it is negatively 
geotropic, but most individuals would orient positively if placed on a dry glass 
or wooden plate. Later, Kanda (1916&) demonstrates for fresh-water snails 
that they are negatively geotropic when their lungs are empty and positively 
geotropic when their lungs are full of air. Olmsted (1917) finds that food is a 
factor in the reversal of the behavior to gravity in Planaria maculata. Adams 
(1903) concludes that earthworms retreat into their burrows during the day- 
time because of their negative phototropism, but they emerge at night not so 



376 Relation" of Watee to the Behaviok of 

much because of darkness as because of their positive phototropism for faint 
light. Wilson (1891) shows that Hydra is negative to bright light and positive 
to dim light. According to McGinnis (1912), Branchipus serraius is positively 
geotropic in light and negatively geotropic in darkness; darkness rather than 
light may furnish the stimulus to this reversal. In studying the reactions of 
Drosophila to gravity, Cole (1917) finds that the response to gravity is much 
less marked in flying than in creeping, where it is very definite. 

Many animals orient in the field in relation to the center of gravity of the 
earth. Loeb (1905) found that some animals turn their heads upward and 
others downward. To this latter class belongs the garden spider, which he 
found may hang in this position in the center of its web for hours. He dis- 
covered the same behavior in some diptera. Shelford (1917) states that such 
animals as the grasshopper usually orient with the head up, while aphids and 
katydids orient with the head down. In the potato beetle the majority of 
larvae and a large number of adults orient with the dorsal side down. 

There is a vast amount of literature dealing upon reversibility in photo- 
tropism through chemical agencies. Loeb (1893 and 1904) proves that it was 
possible to reverse the reactions of a large number of water forms through 
chemicals such as salts, acids, and the like. According to Moore (1912a, 1912&, 
and 1913), phototropism in Daphnia and Diaptomus may be influenced through 
the agency of caffein, strychnin, atropin, acids, alcohol, and ether. Moore 
(1913) says: 

"While negative phototropism in Diaptomus can be reversed by acids, but 
positive phototropism brought about by chemical means can not be reversed by 
strychnin (atropin or caffein)." 

Wolfgang (1912) determines that electrolites influence phototaxis, and 
Kanda (1914) reversed geotropism in Arenicola larvae by means of salts. 



EXPERIMENTS UPON THE ROLE OF WATER IN GEOTROPISM. 

On May 15, at 8 p. m., 21 freshly emerged beetles (Tucson A, g. I) were 
moved to a constant- temperature room and tested 10 times as to their reactions 
to gravity, and in each test all were negative. These geotropic reactions were 
tested in the dark, and if the beetles crawled to the top of the tube, when held 
in a vertical position, they were considered as positive and if they crawled to 
the bottom as negative. The thermograph tracings showed a constant tempera- 
ture of 21° C, with a daily variation of 1° C, throughout the test. Again at 
11 a. m. on May 16, when tested as previously (10 times), they were still 
negative to gravity, and at this time weighed 2.0009 grams; furthermore, on 
May 17 at lO'' 30™ a. m., they weighed 1.9294 grams, and again gave the same 
test to gravity, so that these results proved that the beetles under these con- 
ditions were uniform for this reaction. For experimental purposes these insects 
were divided into three groups. The first group of 7 adults was put into a 
calcium-chloride chamber, which produced so high a rate of evaporation as to 
desiccate them; the second of 7 individuals was subjected to a low rate of 
evaporation by placing wet filter-paper under the bell-jar, so that little water 
was removed from them under these conditions; in the third chamber 7 adults 



The Potato Beetle in a Desert 



377 



were used as a control. In table 12, the results are given, which shows that 
group 1 at the beginning of the test was negative, but by 9*^ 30"° a. m., while 
under the dry bell-jar, all became positive, but when moist conditions were 
restored in the Jar, by 10 a. m. on May 26, they were again negative. In group 2, 
at the beginning, all were negative and remained thus as long as they were kept 
under moist conditions, but at 10 a. m. on May 30, all had become positive. In 



Table 12. — Reversal in the potato beetle to gravity. 






Date and hour of observation. 


a 

V 

o. 
S 

V 

u 

< 


Group 1. 


Group 2. 


Group S. 


o ^ 


o 


o 

>^ 
'C > 

a a 

i) be 




o 
&< 


o 

a =« 




o 

a, 


o 

>ii 

'Z > 

a M 

be ^ 
vbi) 


May 17, 10" 30™ a. m 

May 19, 12 30 p. m 

May 21, 9 30 a. m 

May 22, 10 00 a.m 

May 24, 10 00 a.m 

May 26, 10 00 a.m 

May 28, 10 00 a.m 

May 30, 10 00 a.m 


°c. 
20 
20 
20 
20 
20 
20 
20 
20 


gms. 
0.692 
.573 
.496 
.577 
.682 
.684 
.685 
.683 


p. ct. 



80 

100 

25 

15 








p. ct. 

100 

20 



75 

85 

100 

100 

100 


gms. 
0.640 
.783 
.801 
.810 
.810 
.703 
.594 
.556 


p. ct. 






15 

100 


p.ct. 
100 
100 
100 
100 
100 
100 
85 



gms. 
0.597 
.590 
.586 
.577 
.571 
.570 
.563 
.560 


p. ct. 











30 

100 

100 


p. Ct. 

100 

100 

100 

100 

100 

70 







Note. — In group 1 the conditions in bell-jar were dry on May 17, 19, and 21, and 
moist on the other days. In group 2 said conditions were dry on May 26, 28, and 30, 
and moist on other days. In group 3 said conditions were uniform throughout. 

group 3, which were the control individuals, a gradual loss of weight occurred 
until 10 a. m. on May 28, when all were positive. These results showed clearly 
that reactions to gravity may be reversed through changes in the moisture- 
content of the surrounding medium. 



RELATION OF TEMPERATURE TO THE OUTGO AND 
INTAKE OF WATER. 

An interesting discovery was the determination that there was little absorp- 
tion of water below 12° C. as was shown in a test in which beetles emerging 
from pupation were collected on July 28; they were placed under a bell-jar 
containing wet filter-paper, where they remain until 12 midnight on July 30, 
when equal numbers of insects were placed in two bell-jars, in a refrigerator, at 
a temperature of 10° to 13° C. One bell- jar contained wet filter-paper and the 
other calcium chloride, but weighings made at frequent intervals showed that 
in the humidor there was no appreciable loss during the 84 hours in the 
refrigerator. In another test, desiccated beetles were placed under saturated 
bell-jars in the refrigerator, but weighings made at frequent intervals gave no 
evidence of water-absorption. These results showed how much organisms were 
protected from absorbing water during winter rains, which would otherwise 
result in their freezing, and further demonstrated that desiccation, occurring 
slowly at a low temperature, was a factor in the economy of the organism. 

A similar result was obtained with upper temperature limits. It is known 
that the coagulation temperature of colloids varies with the amount of contained 



378 Eelation" of Water to the Behavior of 

water, a condition with which our results on L. decemlineata agreed generally, 
since the death-point in potato beetles with a high water-content was 58° to 
60° C, and desiccated ones withstood 1° to °5 higher temperature. Bachmet- 
jew (1902) shows that the temperature of the insect's body varied with the 
conditions, namely, moisture, temperature, and the like. If the air was damp, 
the body-temperature was higher than that of the surrounding medium, since no 
evaporation occurred; but if the air was dry it cooled through evaporation. 
He also pointed out that the smaller the percentage of fluids in a unit of the 
living insect body, the lower was the normal congealing-point of the fluids. 
Tower (1906) states that soil-temperatures taken on the savannas of Vera Cruz 
in April 1904, in places where L. decemlineata was aestivating, were frequently 
as high as 60° to 65° C, and that success in passing through these high tem- 
peratures at the end of the dry season depended upon the completeness of the 
physiological changes preceding entrance into hibernation. These results were 
similar to those just given for this insect, which showed that the lower and 
upper temperature limits were influenced through water-relation. 

In studying longevity in insects, Baumberger (1914) shows that the tem- 
perature at which colloidal substances coagulate lowers with a decrease in 
water-content and that long exposure to cold or high temperature may result 
in this decrease in water. He explains that the result of a long exposure to cold 
is the same as short exposure to heat, while intensity of cold shortens the length 
of the period. He also demonstrates that the point of coagulation varies with . 
the water-content of the insects studied. Greely (1901) concludes that: 

" A reduction of the temperature and a loss of the water have similar effects, 
because the cell loses water when the temperature is lowered, as well as when 
the concentration of the surrounding medium is raised." 

The results of Livingston (1903) show for Spirogyra that a cell loses water 
when the temperature is lowered. In discussing the reversal in animal instincts, 
Loeb (1900) concludes that a decrease in temperature has the same physio- 
logical effects as a loss of water. 

METABOLISM AND THE WATER-RELATION. 

The results of various workers show that desiccation modifies the rate of 
metabolism; thus, the alterations in the behavior of the potato beetle may be 
due to differences in metabolic activity, brought about through combined rela- 
tions of water and temperature of the organism. Shelf ord (1913) states that 
the changes in activity of the animals used in his experiments were due to the 
withdrawal of water. 

It is known that anything which disturbs the rate of metabolism in an animal 
alters its response to a stimulus, and that reversed reactions in behavior are 
caused by changes in this metabolic process. According to Jennings (1904), 
Child (1910), Wodsedalek (1911), Allee (1913), Phipps (1915), and others a 
stimulus may change the physiological state of an animal, which produces a 
modified type of reaction. Many depressing agents are also known, such as 
potassium cyanide, chloretone, and a low oxygen content. Baumberger (1914) 
shows that starvation is an agent of this character, since it decreases metabolism 
by removing material to be oxidized. Loeb (1906), Mast (1911), Shelford 
(1914), and others further demonstrate that acids and alkalis increase irri- 



The Potato Beetle in a Deseet 379 

tability. The results of Shelford (1914) and of Chenoweth (1917), however, 
agree most closely with those which are recorded in this paper. Both of these 
observers conclude that a high rate of evaporation increases sensibility or irri- 
tability through loss of water, a condition which might account for the altera- 
tions in the reactions of the potato beetle. 

GENERAL DISCUSSION UPON THE ROLE OF WATER IN 

LIVING THINGS. 

In order to show why such a large number of reactions in the potato beetle 
were controlled by its water-relation, it was considered necessary to review only 
literature which bore directly upon these studies. "It was assuredly not 
chance," to quote Henderson (1913), " that led Thales to found philosophy and 
science with the assertion that water is the origin of all things." He also states 
that the action of water now appears to be a momentous factor in geological 
evolution, and the physiologist has found that water is invariably the principal 
constituent of living organisms. Thus, according to this observer, water makes 
up from 70 to 85 per cent of fishes, about 87 per cent of oysters, 85 per cent of 
apples, 78 per cent of potatoes, and 95 per cent of the edible portion of lettuce. 
It is interesting in this connection to add that my results upon the potato beetle 
show it to contain 80 per cent water. Henderson further says that the organism 
itself is essentially an aqueous solution in which are spread out colloidal sub- 
stances of vast complexity, and as a result of these conditions there is hardly a 
physiological process in which water is not of fundamental importance. Accord- 
ing to Livingston (1903), it is absolutely essential that every living mass of 
protoplasm be saturated with water, since vital phenomena occur solely in 
aqueous solutions. 

Physiologists have long recognized that water is of the greatest importance 
for normal activity of tissues and that all exchanges of material, all supplies of 
food, and metabolic processes in general are dependent upon it. Aberhalden 
and Hall (1908) assert that water is absolutely necessary as a solvent for 
numerous compounds, for it brings into play various chemical reactions, which 
take part in building up and breaking down substances without number ; it is 
also a carrier of nourishment to the body and provides the means for the removal 
of its waste products. In discussing the physical importance of water, Hammar- 
sten and Mendel (1911) show that water by its evaporation is an important 
regulator of temperature. Davenport (1897) states that growth is due chiefly 
to imbibed water, and Estabrook (1910) also demonstrates that growth in 
paramcecium is due almost solely to inhibition of water. MacDougal (1912), 
Lloyd (1905), and others demonstrated that many plants absorb water directly 
from the air. In respect to this subject, in animals the frog has perhaps 
received most attention, and according to Hill (1908) frogs take up water 
through the skin ; they do not drink, for a thirsting frog with its gullet tied 
increases in weight no less than one with the gullet open. He also states that a 
frog can be gradually dried to less than 39 per cent of its normal weight with- 
out fatal results. My own data for the potato beetle show that it can be desic- 
cated to less than 50 per cent and still live, while Catalpa lanigera will die if 
reduced by 25 per cent and the June bug if dried less than 15 per cent of its 
normal weight. 



380 Eelation of Water to the Behavioe of 

It is not true that all animals do absorb water, for my experiments upon the 
scorpion and horned lizard {Phrynosoma comutum) of the Tucson Desert indi- 
cated that these animals would not imbide any aerial water, and even when 
immersed in it no absorption was detected; furthermore, when desiccated no 
difference in weight was observed. A large scorpion lived for more than 2 
tQonths in a desiccator without food, but it probably died of starvation. If 
lizards do not absorb any appreciable amount of water or lose any through 
desiccation, then such a condition might demonstrate why they are distributed 
in a desert as well as in a hot humid region ; therefore, the water-relation would 
not be the determining factor in a lizard's habitat, but the temperature-relation 
should be of greater importance in determining its distribution. This might 
also account for the results of Weese (1917), since he studied the reactions of 
the horned lizard to evaporation and temperature gradients, but found that the 
lizard responded definitely to temperature, while there was no marked reaction 
to evaporation. In this connection the work of Matthews (1913) is important. 
He says: 

" There is a mechanism for rendering mammals tolerably independent of the 
moisture content of their environment, a mechanism most highly developed in 
the reptiles. A mechanism formed by the replacing of the wet skin of the 
amphibian by a dry or scaly skin; the perfecting of the kidneys to maintain 
osmotic pressure of the blood ; the control of the sweat glands and loss of water 
by the intestines ; the developmentofmembranes non-permeable to salts so that 

ammaTs may sit in fresh water an^Mse their salts By this improvement 

reptiles have secured almost complete independence of the water-content of 
their surroundings." 

Water is essential to life, says Babcock (1912), for during the period of 
development it is the most abundant constituent of living organisms. He 
continues : 

" Some of this water is imbibed directly, some of it is taken with solid food 
which is rarely dry, and some of it is formed within the organisms by metabolic 
changes in the organic constituents of the food and tissues, induced by respira- 
tion and other vital processes. The relative amount of water derived from each 
of these sources depends upon the kind of organisms, its period of growth, the 
nature of its food, its environment, and its activities." 

His experiments show that many varieties of insects, such as the clothes-moth, 
the bee-moth, and the flour-beetle, the flour-moth, and others live during all 
stages of development upon foods containing less than 10 per cent of water. 
He concludes that nearly all the water used by insects feeding upon air-dried 
foods is metabolic. In my own experiments upon the potato-beetle and other 
animals there are no data upon metabolic water and its relation to behavior. 

The results of Hegner (1916) further illustrate the water-relation in animals. 
He arranged an experiment upon oviposition in the potato-beetle, so that 35 
batches of eggs were in the sunlight and 15 were in the shade. Those in the sun 
came to nothing, but all in the shade were hatched. It was found that develop- 
ment had started in the sunlight, but that desiccation probably arrested this 
process; therefore he concludes that the advantage of concealment is not so 
great as that secured by shielding the eggs from the desiccating properties of the 
sun. My results show that the majority of adults orient to gravity with their 
dorsal side down, which might explain why eggs are usually deposited on the 
under side of a potato-leaf. 



The Potato Beetle in a Desekt 381 



SUMMARY AND CONCLUSION. 



In general the results indicate for the potato-beetle that : 

( 1 ) The optimum breeding activity of this insect coincides with the highest 
water-content of the atmosphere, since periods of oviposition are exactly con- 
current with those of rain and low rates of evaporation. 

(2) Differences in soil-moisture produce alterations in the water-content 
of these animals which modify their behavior, since beetles will lay their eggs 
sooner if they emerge from a soil of high moisture-content than if they issue 
from a dry soil. 

(3) Egg-production is also modified by differences in the evaporating power 
of the air which surrounds these insects, since a low rate of evaporation en- 
courages oviposition. 

(4) The beetle dies if buried when all its activities are normal, but either 
the summer or winter generation may be buried without injury if previously 
desiccated. 

(5) The adobe soil of the arid region retains a relatively high percentage of 
water and is thus an excellent medium for the sustentation of the life of this 
beetle, as in other desert animals. 

(6) These insects exhibit a physiological behavior not unlike that of trans- 
piration in plants; but further, their tropisms are modified by loss of water, 
which is governed by the evaporating power of the air. 

(7) The evaporating power of the ait surrounding these insects determines 
their behavior through transpiration ; even their responses to light and gravity 
are controlled by evaporation. 

(8) Entrance into hibernation in a desert region may be produced at any 
time through desiccation, except at low temperatures, when little desiccation 
takes place. 

(9) The hibernating period in an arid region is controlled by the duration of 
the dry season, but is dependent upon the length of the winter in a temperate 
region. 

(10) The water-relation is the controlling factor in the emergence of this 
insect from hibernation if the temperature is above 15° C. 

(11) When surrounded by a moist medium (above 15° C), either atmosphere 
or soil, these beetles are positive to light and negative to gravity, but desiccation 
reverses this behavior. 

(12) This insect absorbs very little water below 12° C. ; its death-point under 
a high water-content was found to be 58° to 60° C, but when desiccated it can 
withstand from 1° to 5° C. more of heat. 

(13) Alterations in the behavior of the potato-beetle may be due to differ- 
ences in metabolic activity as influenced through the water-relation. 

(14) This animal also imbibed water directly, but no studies were made upon 
metabolic water. 

We may conclude that Leptinotarsa decemlineata, when introduced from its 
grassland habitat into an arid region, is equilibrated immediately with respect 
to its surroundings, especially in regard to its water and temperature medium ; 
that its behavior is changed to resemble those responses still present in an 
organism long accustomed to a desert complex, and that, since water is the 



382 Eelation of Water to the Behavior of 

limiting factor in an arid region and the prime essential for metabolism, the 
behavior of the potato beetle in a desert is determined chiefly by the water- 
content of its environment. Henderson (1913) states: 

" Water, of its very nature, as it occurs automatically in the process of cosmic 
evolution, is fit, with a fitness no less marvelous and varied than that fitness of 
the organism which has been won by the process of adaptation in the course of 
organic evolution. ... In truth. Darwinian fitness is a perfectly reciprocal 
relationship. In the world of modern science a fit organism inhabits a fit 
environment." 

These results upon the potato beetle indicate that its marvelous fitness and 
adaptation to water is such a " reciprocal relationship." 

The experiments were performed at the Desert Laboratory of the Carnegie 
Institution of Washington, and it is a pleasure to acknowledge my indebtedness 
to its director. Dr. D. T. MacDougal, for his interest manifested. I must also 
acknowledge my great indebtedness to Professor W. L. Tower, of the University 
of Chicago, who made it possible for me to continue this problem at Tucson. 
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